Rectification circuit

ABSTRACT

The present invention sets forth multiple embodiments of an electrical circuit which rectifies alternating current in a manner which results in very little electrical loss. This is in contrast to conventional rectifier circuits that use simple diode configurations which typically give rise to voltage losses from 0.4 volts to 1.0 volts.

DETAILED DESCRIPTION OF THE INVENTION

1. Technical Field

The present invention relates to an electric circuit for rectifying analternating current, more particularly to an electric circuit forrectifying an alternating current with a small loss.

2. Background Art

A rectification circuit has been used as a circuit for converting analternating voltage to a direct voltage.

The conventional rectification circuit is comprised of a silicon diode,a schottky-barrier diode, or the like.

In the conventional circuit, however, a forward voltage Vf of a diode isapproximately 0.4V to 1.0V, as shown in FIG. 3 showing a relationshipbetween the voltage Vf and a current If. Therefore, the voltage drop, inother words, a loss in the diode of the rectification circuit, is large.As a result, inefficient rectification has been a problematical matter.

The present invention has been made in consideration of the above, andit is an object of the present invention to provide an electric circuitwhich can rectify an alternating current with a small loss.

DISCLOSURE OF INVENTION

To achieve the above described object, an electric circuit according toa first aspect of the present invention comprises a transistor and acontrol circuit connected to said transistor, and is characterized inthat said transistor comprises a current path and a control terminal,receives a target voltage to be rectified at one end of said currentpath, and is controlled by said control circuit to be activated orinactivated to output a rectified voltage at the other end of saidcurrent path; and

said control circuit is connected to at least one end of said currentpath of said transistor and said control terminal, activates saidtransistor when a reverse voltage is applied to said current path,inactivates said transistor when a forward voltage is applied to saidcurrent path, and controls a signal to be applied to said controlterminal for activating or inactivating said transistor to make saidtransistor rectify said target voltage.

According to the electric circuit of the first aspect of the presentinvention, the transistor is activated when the voltage applied to thecurrent path of the transistor is a reverse voltage, and is inactivatedwhen it is a forward voltage. Therefore, only a voltage having onepolarity is applied to a load which is connected to the transistor. And,a forward voltage is applied to the current path when the transistor isinactivated, therefore, a high withstanding voltage can be obtained.

The electric circuit according to a second aspect of the presentinvention comprises a transistor and a control circuit connected to saidtransistor, and is characterized in that said transistor comprises acurrent path and a control terminal, receives a target voltage to berectified at one end of said current path, and outputs a rectifiedvoltage at the other end of said current path by being activated orinactivated in accordance with control of said control circuit; and

said control circuit is connected to both ends of said current path andsaid control terminal, detects the potential difference between the bothends of said current path, and controls a signal to be applied to saidcontrol terminal for activating or inactivating said transistor, so asto activate said transistor when a reverse voltage of said transistor isapplied to said current path of said transistor and inactivate saidtransistor when a forward voltage of said transistor is applied to saidcurrent path, to make said transistor rectify said target voltage.

The electric circuit according to a third aspect comprises a transistorand a control circuit connected to said transistor, and is characterizedin that said transistor comprises a current path and a control terminal,receives a target voltage to be rectified at one end of said currentpath, and outputs a rectified voltage to the other end of said currentpath by being activated or inactivated in accordance with control ofsaid control circuit; and

said control circuit is connected to both ends of said current path andsaid control terminal, detects the potential difference between the bothends of said current path, and controls a signal to be applied to saidcontrol terminal for activating or inactivating said transistor so as toactivate said transistor when a reverse voltage is applied to saidcurrent path of said transistor and inactivate said transistor when aforward voltage is applied to said current path to make said transistorrectify said target voltage.

According to the electric circuit of the second and third aspects of thepresent invention, the voltage which is applied between the both ends ofthe current path of the transistor or the polarity of the voltage isdetected, and the transistor is activated when the voltage is in thereverse direction and the transistor is inactivated when the voltage isin the forward direction. Therefore, only voltage in one polarity isapplied to a load which is connected to the other end side of thecurrent path of the transistor. And, the forward voltage is applied tothe current path when the transistor is inactivated, therefore, a highwithstanding voltage can be obtained.

In thus structured electric circuit, there is a way toactivate/inactivate the transistor based on values for the suppliedtarget voltage to be rectified or its polarity. However, a reversecurrent flow is caused by this method because the source voltage becomeslower than the voltage at the load while the transistor is beingactivated, when a capacitor or a battery is used as the load retainingthe voltage. By the present invention, the target voltage to berectified can be rectified without such a problem because the voltage tobe applied to the current path of the transistor is detected.

Said transistor is, for example, a bipolar transistor. In this case,both ends of said current path are the emitter and collector of saidbipolar transistor, said control terminal is the base of said bipolartransistor, and said control circuit comprises means for detectingvoltage and/or its polarity between said emitter and said collector, andfor supplying a voltage and a current to said base.

If said bipolar transistor is an NPN type bipolar transistor:

one end of said current path is emitter of said NPN bipolar transistor,the other end of said current path is collector of said NPN bipolartransistor, and said control terminal is base of said NPN bipolartransistor; and

said control circuit supplies a voltage and a current for activatingsaid NPN transistor to said base when potential in positive polarity,which is higher than that applied to said collector, is applied to saidemitter, and supplies a voltage and a current for inactivating said NPNtransistor to said base when voltage in positive polarity, which islower than that applied to said collector, is applied to said emitter.

If said bipolar transistor is a PNP type bipolar transistor:

one end of said current path is emitter of said PNP bipolar transistor,the other end of said current path is collector of said PNP bipolartransistor, and said control terminal is base of said PNP bipolartransistor; and

said control circuit supplies a voltage and a current for activatingsaid PNP transistor to said base when potential in positive polarity,which is higher than that applied to said emitter, is applied to saidcollector, and supplies a voltage and a current for inactivating saidPNP transistor to said base when voltage in positive polarity, which islower than that applied to said emitter, is applied to said collector.

Said bipolar transistor comprises the emitter and the collector bothhaving substantially the same thickness of semiconductor layers.According to such a structure, the emitter and the collector are notdistinguished substantially, and it can save current amplificationfactor largely during activation. Moreover, high withstanding voltagecan be obtained.

Said transistor may be replaced with a field effect transistor.

In this case, both ends of said current path are source and drain ofsaid field effect transistor, said control terminal is gate of saidfield effect transistor, and said control circuit comprises means fordetecting voltage and/or its polarity between said source and saiddrain, and for applying a control voltage to said gate in accordancewith the detected voltage.

If said field effect transistor is an N-channel type field effecttransistor:

one end of said current path is source of said N-channel field effecttransistor, the other end of said current path is drain of saidN-channel field effect transistor, and said control terminal is gate ofsaid N-channel field effect transistor; and

said control circuit comprises means for applying an activation voltageto said gate when voltage in positive polarity, which is higher thanthat applied to said drain, is applied to said source, and for supplyingan inactivation voltage to said gate when voltage in positive polarity,which is lower than that applied to said drain, is applied to saidsource.

If said field effect transistor is a P-channel type field effecttransistor;

said control circuit comprises means for applying voltage for activatingsaid P-channel field effect transistor to said gate when voltage inpositive polarity, which is lower than that applied to said drain, isapplied to said source, and applying voltage for inactivating saidP-channel field effect transistor to said gate when voltage in positivepolarity, which is higher than that applied to said drain, is applied tosaid source.

Said control circuit comprises, for example, an amplification circuit,such as an operational amplifier, whose one input terminal is connectedto one end of said current path of said transistor, whose other inputterminal is connected to the other end of the current path of saidtransistor, and whose output terminal is connected to said controlterminal of said transistor. In this case, a diode, which is connectedparallel in reverse between said one and the other input terminals ofsaid amplification circuit, and a constant current source, which isinserted between said one input terminal and the one end of said currentpath or between said other input terminal and the other end of saidcurrent path, may be further disposed thereon.

The operational amplifier may be one which performs as not only anamplifier but also a comparator. In other words, it may be one whoseoutput voltage is saturated in accordance with input voltage.

The electric circuit according to a fourth aspect of the presentinvention comprises a transistor and a control circuit connected to saidtransistor, and is characterized in that said transistor comprises acurrent path and a control terminal, receives a target voltage to berectified at one end of said current path, and is controlled by saidcontrol circuit to be activated and inactivated to output a rectifiedvoltage to the other end of said current path; and

said control circuit is connected to said current path and said controlterminal of said transistor, and controls a signal to be applied to saidcontrol terminal in accordance with the direction of the current flowingthrough a node between one end of said current path and an externalcircuit, for activating or inactivating said transistor to make saidtransistor rectify said target voltage.

In the electric circuit according to the fourth aspect of the presentinvention, the transistor is activated and inactivated in accordancewith the direction of the current flowing at the connection node betweenthe current path of the transistor and the external circuit. When thetransistor is activated, said current flows via the current path of thetransistor and is supplied to a load circuit. Therefore, the rectifiedcurrent can be applied to the load. Moreover, because forward voltage isapplied when the transistor is inactivated, high withstanding voltagecan be obtained.

Said transistor is, for example, a bipolar transistor. In this case,both ends of said current path are emitter and collector of said bipolartransistor, and said control terminal is base of said bipolartransistor. Said control circuit supplies a voltage and a current tosaid base, and activates said bipolar transistor.

If said bipolar transistor is an NPN type bipolar transistor;

one end of said current path is emitter of said NPN bipolar transistor,the other end of said current path is collector of said NPN bipolartransistor, and said control terminal is base of said bipolartransistor. Said control circuit detects the direction of the currentflowing at a node between said emitter and said external circuit, andsupplies a voltage and a current for activating said NPN transistor whenthe current in the predetermined direction is detected.

In this case, a diode may be connected between said emitter and saidcollector or between said emitter and said base so that the current inthe predetermined direction flow at said node even if said NPN bipolartransistor is not activated.

If said bipolar transistor is a PNP type bipolar transistor;

one end of said current path is emitter of said PNP bipolar transistor,the other end of said current path is collector of said PNP bipolartransistor, and said control terminal is base of said PNP bipolartransistor. Said control circuit detects the direction of the currentflowing at the node between said emitter and said external circuit, andsupplies a voltage and a current for activating said PNP transistor tosaid base when the current in the predetermined direction are detected.

In those cases, a diode may be connected between said emitter and saidcollector or between said emitter and said base so that the current inthe predetermined direction flow at said node even if said NPN bipolartransistor is not activated.

Said transistor is, for example, a field effect transistor;

both ends of said current path are source and drain of said field effecttransistor, and said control terminal is gate of said field effecttransistor; and

said control circuit comprises means for applying the gate voltage,which activates said field effect transistor in an area, to said gate.

If said field effect transistor is an N-channel type field effecttransistor, for example, one end of said current path is source of saidN-channel field effect transistor, the other end is drain of saidN-channel field effect transistor, and said control terminal is gate ofsaid field effect transistor. Said control circuit comprises means forapplying voltage, which activate said N-channel field effect transistor,to said gate when the current flowing at the node between said sourceand said external circuit are in the predetermined direction.

If said field effect transistor is the N-channel type field effecttransistor, said control circuit comprises means for detecting, forexample, the current flowing from said source to said drain via aparasitic diode to activate said N-channel field effect transistor.

A diode may be connected between said source and said drain, or avoltage regulation diode may be connected between said gate and saidsource.

If said field effect transistor is a P-channel type field effecttransistor, for example, one end of said current path is source of saidP-channel field effect transistor, the other end thereof is drain ofsaid P-channel field effect transistor, and said control terminal isgate of said P-channel field effect transistor. Said control circuitcomprises means for applying voltage, which activates said P-channelfield effect transistor, to said gate when the current flowing at thenode between said source and said external circuit are in thepredetermined direction.

Said control circuit may comprise means for detecting a current flowingfrom said drain to said source via a parasitic diode of said P-channelfield effect transistor to activate said P-channel field effecttransistor.

In those cases, a diode may be connected between said source and saiddrain, or a voltage regulation diode may be connected between said gateand said source.

Said control circuit comprises, for example, a transformer having aprimary winding which is connected to one end of said current path ofsaid transistor and a secondary winding which is magnetically connectedto said primary winding, and a bias circuit which is connected to saidsecondary winding of said transformer and controls a signal to besupplied to said control terminal of said transistor in accordance withcurrent which is generated at said secondary winding.

Said control circuit may comprise, for example, means for converting theinductive current at said secondary winding into a voltage signal toapply it to said control terminal. In this case, said control circuitcomprises, for example, a conversion circuit for converting saidinductive current at the secondary winding into a voltage signal, andmeans for amplifying the voltage signal converted by said conversioncircuit and applying the amplified signal to said control terminal ofsaid transistor.

Said control circuit comprises, for example, an active element whichrequires electricity, and said rectified voltage is supplied to saidactive element as the electricity.

The electric circuit according to a fifth aspect of the presentinvention comprises a transistor and a control circuit connected to saidtransistor, and is characterized in that said transistor comprises acurrent path and a control terminal, receives a target voltage to berectified at one end of said current path from the power source, isconnected to a resistance load via the other end of said current path,and is controlled by said control circuit to be activated andinactivated to output a rectified voltage to the other end of saidcurrent path; and

a predetermined reference potential is applied to said control terminal.

This is a very simple structure, however, the rectified voltage can beapplied to the resistance road.

For example, said control terminal of said transistor, said powersource, and said load are grounded at a substantially common point.

It is to be desired that said control circuit should activate saidtransistor under its saturation. Under the saturation, the emitter andthe collector of the bipolar transistor have almost the same potential.Therefore, the voltage drop in the transistor seldom occurs while thebipolar transistor is activated, that is, at the moment of applying thevoltage which is rectified by the load. Therefore, it is capable ofefficient rectification with a small loss.

In the first to fifth inventions, the target voltage to be rectified maybe an alternate signal or an alternate signal (a pulsating current) towhich a direct current component is added, and its waveform may be anyone of the sine wave, the triangle wave, the rectangular wave, or thelike.

The meaning of “connected” here is not limited to “wirebound”. Itincludes cases of physical or electrical connection with the magnetism,an electric field, the light, or the like. For example, if a transistor,which is activated and inactivated in accordance with the amount of thelight applied to its control terminal, is used, a control circuit andthe control terminal are connected each other with the light. If atransistor which responds to the magnetic field of a Hall element, orthe like, its control terminal and the control circuit are connectedeach other with the magnetic field.

The electric circuit according to a sixth aspect of the presentinvention comprises a transistor and a control circuit connected to saidtransistor, and is characterized in that said transistor comprises acurrent path and a control terminal, receives a target voltage to berectified at one end of said current path, and is controlled by saidcontrol circuit to be activated or inactivated to output rectifiedvoltage to the other end of said current path; and

said control circuit, which is connected to at least one end of saidcurrent path of said transistor and said control terminal, makes saidtransistor rectify said target voltage to be rectified by controlling asignal to be applied to said control terminal to activate or inactivatesaid transistor so that said transistor is activated when a reversevoltage is applied to said current path and said transistor isinactivated when a forward voltage is applied to said current path,

said electric circuit is characterized in that said control circuitcomprises:

a transformer comprising a primary winding to which electricity isprovided, a secondary winding, which is inductively connected to saidprimary winding, for taking an output to be supplied to a load, and adetection winding, which is inductively connected to said primarywinding, showing an output corresponding to an output of said secondarywinding, and

detection means for inputting an output voltage of said secondarywinding and an output voltage of said detection winding, for detectingwhether said reverse voltage is applied to said current path and whethersaid forward voltage is applied to said current path, and for applying asignal indicating a result of the detection to said control terminal ofsaid transistor.

The electric circuit according to a seventh aspect of the presentinvention comprises a transistor and a control circuit connected to saidtransistor, and is characterized in that said transistor comprises acurrent path and a control terminal, receives a target voltage to berectified at one end of said current path, and is controlled by saidcontrol circuit to be activated or inactivated to output rectifiedvoltage to the other end of said current path; and

said control circuit, which is connected to at least one end of saidcurrent path of said transistor and said control terminal, makes saidtransistor rectify said target voltage to be rectified by controlling asignal to be applied to said control terminal to activate or inactivatesaid transistor so that said transistor is activated when the reversevoltage is applied to said current path and said transistor isinactivated when the forward voltage is applied to said current path,

said electric circuit is characterized in that said control circuitcomprises:

a first transformer comprising a primary winding to which an electricityis provided, and a second winding, which is inductively connected tosaid primary winding, for taking an output to be supplied to a load;

a second transformer, which is disposed being parallel to said firsttransformer while being insulated from said first transformer,comprising a first winding to which an electricity is provided, and adetection winding, which is inductively connected to said primarywinding, showing an output corresponding to an output of said secondarywinding of said first transformer; and

detection means for inputting an output voltage of said secondarywinding and an output voltage of said detection winding, for detectingwhether said reverse voltage is applied to said current path and whethersaid forward voltage is applied to said current path, and for applying asignal indicating a result of the detection to said control terminal ofsaid transistor.

The electric circuits according to the sixth and the seventh aspects canrectify the alternate voltage output from the transformer.

The electric circuit according to an eighth aspect of the presentinvention comprises a semiconductor switching element and a controlcircuit for controlling said semiconductor switching element, and ischaracterized in that said semiconductor switching element comprises acurrent path whose one end is connected to a power source side and theother end is connected to a load side, and is controlled by said controlcircuit to be activated and inactivated; and

said control circuit is connected to both ends of said current path ofsaid semiconductor switching element, detects voltage to be applied tosaid current path, and supplies a signal to said semiconductor switchingelement in accordance with a result of the detection to activate orinactivate said semiconductor switching element.

For example, a bipolar transistor, a field effect transistor, a phototransistor, a Hall element, a thyristor, or the like may be used as thesemiconductor switching element.

The control circuit applies a control signal to the semiconductorswitching element in accordance with the characteristics of thesemiconductor switching element. For example, if the semiconductorswitching element is the bipolar transistor, a voltage and a current tobe supplied to base are controlled to activate and inactivate thebipolar transistor. If the semiconductor switching element is the fieldeffect transistor, an electric field to be applied to gate is controlledto activate and inactivate the field effect transistor. If there is agate electrode, voltage to be applied to the gate electrode iscontrolled. If the semiconductor switching element is the phototransistor, quantity (or strength) of the light to be irradiated to baseis controlled to activate and inactivate the photo transistor. If thesemiconductor switching element is the Hall element, a magnetic field(magnetic flux) is controlled to activate and inactivate the Hallelement.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a circuit diagram showing a rectification circuit according toan embodiment of the present invention.

FIGS. 2(A) to (E) are timing charts for explaining an operation of therectification circuit shown in FIG. 1.

FIG. 3 a graph showing ground characteristics of emitter of an NPNbipolar transistor and current/voltage characteristics of a diode.

FIG. 4 is a circuit diagram showing a concrete example of components ofthe rectification circuit shown in FIG. 1.

FIGS. 5(A) and (B) are circuit diagrams showing concrete examples ofcomponents of the rectification circuit shown in FIG. 1.

FIGS. 6(A) to (C) are timing charts showing operations of therectification circuits shown in FIGS. 5(A) and (B).

FIG. 7 is a circuit diagram showing a concrete example of components ofthe rectification circuit shown in FIG. 1.

FIG. 8 is a circuit diagram showing an example of a modified circuit ofthe rectification circuit shown in FIG. 4.

FIGS. 9(A) and (B) are circuit diagrams showing examples of modifiedcircuits of the rectification circuits shown in FIGS. 5(A) and (B).

FIG. 10 is a circuit diagram showing an example of a modified circuit ofthe rectification circuit shown in FIG. 7.

FIGS. 11(A) to (E) are timing charts showing the basic operations of therectification circuits shown in FIGS. 8 to 10.

FIG. 12 is a circuit diagram showing an example of a modified circuit ofthe rectification circuit shown in FIG. 4.

FIG. 13 is a circuit diagram showing an example of a modified circuit ofthe rectification circuits shown in FIGS. 5(A) and (B).

FIG. 14 is a circuit diagram showing an example of a modified circuit ofthe rectification circuit shown in FIG. 7.

FIG. 15 is a circuit diagram showing an example of a modified circuit ofthe rectification circuit shown in FIG. 12.

FIG. 16 is a circuit diagram showing an example of a modified circuit ofthe rectification circuit shown in FIG. 13.

FIG. 17 is a circuit diagram showing an example of a modified circuit ofthe rectification circuit shown in FIG. 14.

FIG. 18 is a circuit diagram showing an example of a modified circuit ofthe rectification circuit shown in FIG. 13.

FIG. 19 is a circuit diagram showing an example of a modified circuit ofthe rectification circuit shown in FIG. 14.

FIG. 20 is a circuit diagram showing an example of a modified circuit ofthe rectification circuit shown in FIG. 4.

FIG. 21 is a circuit diagram showing an example of a modified circuit ofthe rectification circuit shown in FIG. 8.

FIGS. 22(A) and (B) are circuit diagrams showing examples of modifiedcircuits of the rectification circuits shown in FIGS. 5(A) and (B).

FIGS. 23(A) and (B) are circuit diagrams showing examples of modifiedcircuits of the rectification circuits shown in FIGS. 9(A) and (B).

FIG. 24 is a circuit diagram showing an example of a modified circuit ofthe rectification circuit shown in FIG. 7.

FIG. 25 is a circuit diagram showing an example of a modified circuit ofthe rectification circuit shown in FIG. 10.

FIG. 26 is a circuit diagram showing an example of a modified circuit ofthe rectification circuit shown in FIG. 12.

FIG. 27 is a circuit diagram showing an example of a modified circuit ofthe rectification circuit shown in FIG. 15.

FIG. 28 is a circuit diagram showing an example of a modified circuit ofthe rectification circuit shown in FIG. 13.

FIG. 29 is a circuit diagram showing an example of a modified circuit ofthe rectification circuit shown in FIG. 16.

FIG. 30 is a circuit diagram showing an example of a modified circuit ofthe rectification circuit shown in FIG. 14.

FIG. 31 is a circuit diagram showing an example of a modified circuit ofthe rectification circuit shown in FIG. 17.

FIG. 32 is a circuit diagram showing another example of therectification circuit of the present invention.

FIGS. 33(A) to (C) are timing charts for explaining operations of therectification circuit shown in FIG. 32.

FIG. 34 is a circuit diagram showing an example of a rectificationcircuit comprising an OP-amp which is powered by a rectified voltage.

FIG. 35 is a circuit diagram showing an example of a rectificationcircuit comprising an OP-amp which is powered by a rectified voltage.

FIG. 36 is a circuit diagram showing one embodiment of a rectificationcircuit for a resistance load.

FIG. 37 is a circuit diagram showing one embodiment of a rectificationcircuit for a resistance load.

FIG. 38 is a circuit diagram showing one embodiment of a rectificationcircuit for a resistance load.

FIG. 39 is a diagram showing one example of the structural elementsforming a rectification circuit which activates and inactivates atransistor with an output from a secondary winding of a transformer torectify an alternating current.

FIGS. 40(A) and (B) are timing charts for explaining operations of therectification circuit shown in FIG. 39.

FIG. 41 is a diagram showing an example of the structural elementsforming a rectification circuit which activates and inactivates atransistor with an output from a secondary winding of a transformer torectify an alternating current.

FIG. 42 is a diagram showing one example of the structural elementsforming a transformer.

FIGS. 43(A) to (E) are timing charts for explaining operations of therectification circuit shown in FIG. 41.

FIG. 44 is a diagram showing an example of the structural elementsforming a rectification circuit which activates and inactivates atransistor with an output from a secondary winding of a transformer torectify an alternating current.

FIG. 45 is a diagram showing an example of the structural elementsforming a rectification circuit which activates and inactivates atransistor with an output from a secondary winding of a transformer torectify an alternating current.

FIGS. 46(A) and (B) are diagrams showing examples of the structuralelements forming rectification circuits which activate and inactivate atransistor with an output from a secondary winding of a transformer torectify an alternating current.

FIGS. 47(A) and (B) are diagrams showing examples of the structuralelements forming rectification circuits which activate and inactivate atransistor with an output from a secondary winding of a transformer torectify an alternating current.

FIGS. 48(A) and (B) are diagrams showing examples of the structuralelements forming rectification circuits which activate and inactivate atransistor with an output from a secondary winding of a transformer torectify an alternating current.

FIG. 49 is a diagram showing an example of the structural elementsforming a rectification circuit which activates and inactivates atransistor with an output from a secondary winding of a transformer torectify an alternating current.

FIG. 50 is a diagram showing an example of the structural elementsforming a rectification circuit which activates and inactivates atransistor with an output from a secondary winding of a transformer torectify an alternating current.

FIGS. 51(A) and (B) are diagrams showing examples of the structuralelements forming rectification circuits which activate and inactivate atransistor with an output from a secondary winding of a transformer torectify an alternating current.

FIGS. 52(A) and (B) are diagrams showing examples of the structuralelements forming rectification circuits which activate and inactivate atransistor with an output from a secondary winding of a transformer torectify an alternating current.

FIGS. 53(A) and (B) are diagrams showing examples of the structuralelements forming rectification circuits which activate and inactivate atransistor with an output from a secondary winding of a transformer torectify an alternating current.

FIG. 54 is a diagram showing one example of the structural elementsforming a rectification circuit which activates and inactivates atransistor with an output from a secondary winding of a transformer torectify an alternating current.

FIG. 55(A) is a circuit diagram showing an example of the structuralelements forming a full-wave rectification circuit comprisingbridge-connected rectification circuits, and FIG. 55(B) is a circuitdiagram showing an example of the structural elements forming afull-wave rectification circuit comprising a transformer, whosesecondary winding has a middle point, and two rectification circuits.

FIGS. 56(A) to (C) are circuit diagrams showing examples ofrectification circuits having a plurality of transistors which areconnected parallel with each other.

FIG. 57 is a circuit diagram showing an example of a rectificationcircuit having a plurality of transistors which are cascaded.

FIG. 58 is a circuit diagram showing an example of the structuralelements forming a rectification circuit using an optically controllabletransistor.

FIG. 59 is a diagram showing an example of a bipolar transistor.

FIG. 60 is a diagram showing an example of a field effect transistor.

FIG. 61 is a diagram showing the characteristics of the rectificationcircuit which FIG. 12 exemplifies.

FIG. 62 is a diagram showing the characteristics of the rectificationcircuit which FIG. 14 exemplifies.

BEST MODE FOR CARRYING OUT THE INVENTION

A best mode for carrying out the invention will now be described withreference to accompanying drawings.

(Rectification Circuit Using NPN Bipolar Transistor)

FIG. 1 is a circuit diagram showing a rectification circuit according toan embodiment of the present invention.

The rectification circuit is comprised of an NPN bipolar transistor 11,and a control circuit 13 connected to base B of the bipolar transistor11.

Emitter E of the bipolar transistor 11 is connected to an alternatingcurrent source 15, and a collector C of the bipolar transistor 11 isconnected to a load 17.

The control circuit 13 is connected to the alternating current source15. When the polarity of a source voltage is positive, a bias voltage(which is satisfactorily higher than an emitter voltage), which is foractivating the bipolar transistor 11 under saturation, and an electriccurrent are applied to the base B. On the other hand, when the polarityof an output voltage from the alternating current source 15 is negative,a very low voltage (whose polarity is negative against the emittervoltage), which is enough for inactivating the bipolar transistor 11, isapplied to the base B to inactivate the bipolar transistor 11.

When the load 17 has its own voltage as in the case where the load 17 isa secondary battery, the control circuit 13 applies the bias voltage(which is satisfactorily higher than the emitter voltage), which isenough for activating the bipolar transistor 11 under saturation, andthe electric current to the base B when the emitter voltage is higherthan a collector voltage (when the emitter voltage is higher than thecollector voltage while the polarity of the emitter voltage ispositive). On the other hand, when the emitter voltage is lower than thecollector voltage, the very low voltage (whose polarity is negativeagainst the emitter voltage) which is enough for inactivating thebipolar transistor 11 is applied to the base B to inactivate the bipolartransistor 11.

An operation of the rectification circuit shown in FIG. 1 will now bedescribed with reference to the timing charts shown in FIGS. 2(A) to(E).

FIG. 2(A) shows the waveform of the source voltage output from thealternating current source 15. FIG. 2(B) shows the waveform of a voltage(a control voltage) for a control signal output from the control circuit13. FIG. 2(C) shows activated/inactivated periods of the bipolartransistor 11. FIG. 2(D) shows waveform of a voltage to be appliedbetween the emitter and the collector of the bipolar transistor 11. FIG.2(E) shows the waveform of a voltage to be applied to the load 17.

First, when the polarity of the source voltage shown in FIG. 2(A)becomes positive (more precisely, when the emitter voltage becomeshigher than the collector voltage), the control circuit 13 applies thecontrol signal of a positive polarity, which is shown in FIG. 2(B), tothe base B of the bipolar transistor 11. In response to the controlsignal, the bipolar transistor 11 is activated as shown in FIG. 2(C).

At that time, a voltage higher than the voltage applied to the collectorC is applied to the emitter E of the bipolar transistor 11, unlike inthe ordinary case (where the voltage applied to the collector C ishigher than the voltage applied to the emitter E). Thus, the bipolartransistor 11 functions as, so called, an inverse transistor. However,the bipolar transistor 11 can retain satisfactorily large currentamplification factor (hfe), and supply a current to the current pathbetween the emitter E and the collector C which is satisfactorilygreater than a bias current (base current).

Since the driving ability of the control circuit 13 is very high,considerable minority carriers are implanted into the base B of thebipolar transistor 11, and the bipolar transistor 11 is operated underthe saturation. As shown in the characteristic diagram of FIG. 3, thevoltage between the emitter E and the collector C of the bipolartransistor 11 is approximately 0 (shunted) under the saturation, and thevoltage applied to the emitter E is almost equal to the voltage appliedto the collector C. Moreover, those voltages are much lower than theforward voltage for the diode which is shown by a broken line.

Therefore, the voltage drop in the bipolar transistor 11 isapproximately 0 as shown in FIG. 2(E), and a voltage which is almostequal to the source voltage is applied to the load 17 as shown in FIG.2(D).

On the other hand, when the polarity of the source voltage shown in FIG.2(A) becomes negative, the control circuit 13 supplies a control signalhaving a negative polarity to the base B of the bipolar transistor 11,as shown in FIG. 2(B). Thus, the bipolar transistor 11 is inactivated asshown in FIG. 2(C), a ground voltage is applied to the load 17 as shownin FIG. 2(E), and the source voltage is applied between the emitter Eand the collector C as shown in FIG. 2(D) (FIG. 2(D) shows the voltageapplied to the collector C and its standard voltage being applied to theemitter E). At the same time, the bipolar transistor 11 shows forwardconnection, and a withstanding voltage, which is mainly determined by awithstanding voltage of PN junction between the collector C and the baseB, can be obtained.

As a result of such processing being repeated, a half-wave rectifiedvoltage is applied to the load 17 as shown in FIG. 2(E).

According to the structure shown in FIG. 1, a voltage drop between theemitter E and the collector C becomes approximately 0 (for example,around 5 mV to 40 mV) when the bipolar transistor 11 is activated. Thus,the alternating voltage can be rectified with a small loss.

Moreover, a high withstanding voltage which is determined by awithstanding voltage between the collector C and the base B can beobtained when the bipolar transistor 11 is inactivated.

Furthermore, because the bipolar transistor 11 is switched on or off atthe time the target voltage to be rectified is nearly 0, the overshootand the undershoot does not occur in a rectified voltage.

It is preferred that the single bipolar transistor be used as thebipolar transistor 11. A transistor having so called Darlingtonstructure is not desirable one because a bias current (base current)does not flow when the transistor is activated.

The target voltage to be rectified is not limited to a sine wave voltagesuch as that shown in FIG. 2(A). A triangular or rectangular wavevoltage, or the like may be used. A voltage whose average value is not0, in other words, a voltage having an alternating current component towhich a direct current component has been added, may be used.

A concrete example of the control circuit 13 will now be described withreference to FIG. 4.

This example is one in which the control circuit 13 is comprised of anOP-amp (operational amplifier) 21.

In FIG. 4, an output terminal of the OP-amp 21 is connected to the baseB of the NPN bipolar transistor 11 via a resistor 23 for regulating(limiting) current. A positive input terminal of the OP-amp 21 isconnected to the emitter E of the bipolar transistor, and a negativeinput terminal thereof is connected to the collector C of the bipolartransistor via a constant current source 25. Further, a diode 27 a and adiode 27 b, which are parallel with and opposed to each other, areconnected between the positive input terminal and the negative inputterminal.

The OP-amp 21 has the ability to drive a satisfactorily large currentwhich is larger than (may be twice as large as) the bias current for thebipolar transistor. The ground (reference) potential of the powersupplied to the OP-amp 21 from the power source is designed to coincidewith the emitter potential of the bipolar transistor 11 (the groundsource to be supplied to the OP-amp 21 may be supplied to the emitter Eif the power source is single).

A portion enclosed by a broken line 14 in FIG. 4, that is, the bipolartransistor 11, the OP-amp 21, the resistor 23, a constant currentcircuit 25, and the diodes 27 a and 27 b form an integrated circuit(IC). This IC 14 comprises a power source terminal to which the targetvoltage to be rectified is applied, an output terminal to which therectified voltage is applied, and two source terminals VDD and VSS forthe OP-amp 21.

In this structure, when a voltage of the emitter E of the bipolartransistor 11 becomes higher than a voltage for the collector C inpositive polarity, a forward voltage is applied to the diode 27 a, and areverse voltage is applied to the diode 27 b. As a result, the voltagedrop, due to the forward current in the diode 27 a occurs between theinput terminals of the OP-amp 21. The OP-amp 21 amplifies the voltageand applies a control signal having a positive polarity to the base B ofthe bipolar transistor 11. Thus, the bipolar transistor 11 is activatedand is operated in a saturation area, the emitter E and the collector Cbecome conductive and voltages for the emitter E and the collector Cbecome almost equal to each other. Therefore, the source voltage isapplied to the load 17 with almost no loss.

The forward current in the diode 27 a is regulated to be constant by theconstant current source 25 to prevent the OP-amp 21 and the diode 27 afrom being broken.

When the polarity of the source voltage becomes negative and the voltagefor the emitter E of the bipolar transistor 11 becomes lower than thevoltage for the collector C in positive polarity, a reverse voltage isapplied to the diode 27 a and a forward voltage is applied to the diode27 b. As a result, the voltage drop due to the forward current in thediode 27 b occurs between both the input terminals of the OP-amp 21. Thevoltage is amplified by the OP-amp 21 and a control signal having anegative polarity is applied to the base of the bipolar transistor 11.In response to the control signal, the bipolar transistor 11 isinactivated, and almost the whole source voltage is applied between theemitter E and the collector C of the bipolar transistor 11 because theemitter E and the collector C become non conductive, and the groundvoltage is applied to the load 17.

The forward current in the diode 27 b is regulated to be constant by theconstant current source 25 to prevent the OP-amp 21 and the diode 27 bfrom being broken.

In such a manner, also the rectification circuit shown in FIG. 4 canrectifies the alternating source voltage efficiently, as shown in FIGS.2(A) to (E).

Furthermore, it is unnecessary for externally supplying a control signalto the IC 14.

In this embodiment, the bipolar transistor 11 is switched on and off inresponse to the polarity of the voltage between the emitter E and thecollector C, therefore, a reverse current is prevented from flowing evenif the load 17 has a voltage. For example, if the bipolar transistor 11is switched on and off merely in response to the polarity of an outputvoltage from the alternating current source 15 if the load 17 is asecondary battery having a constant voltage, an electric current flowsin reverse (the battery is discharged) when the source voltage is lowerthan an output voltage of the secondary battery. However, such a problemdoes not occur with the structure shown in FIG. 4.

The constant current source 25 may be replaced with a resistor forregulating the current, a constant current diode, or the like. Anarbitrary diode may be used instead of the operational amplifier.

The group of the diodes 27 a and 27 b may be replaced with Zener diodesor resistors.

FIGS. 5(A) and (B) show other examples of the rectification circuit.

In these examples, the control circuit 13 of the rectification circuitis comprised of a transformer (hereinafter referred as a CT (CurrentTransformer)) 31 and an OP-amp 33.

A primary winding of the current transformer 31 intervenes between acurrent path from the power source 15 and the emitter E of the bipolartransistor 11.

In FIG. 5(A), a diode 11 b is connected between the emitter E and thecollector C of the bipolar transistor 11 so that the direction from theemitter E to the collector C is the forward direction. A shottky-barrierdiode, a first recovery diode, or the like may be connectedtherebetween, instead of the diode 11 b.

In FIG. 5(B), the diode 11 b is connected between the emitter E and thebase B of the bipolar transistor 11 so that the direction from theemitter E to the base B is the forward direction.

A secondary winding of the current transformer 31 is magneticallyconnected to the primary winding, and one end thereof is connected tothe power source 15. The primary winding generates an electromotiveforce and the secondary winding generates a reversed electromotive force(showing an additive polarity).

Diodes 35 for regulating the voltage, which are opposite in directionfrom each other, are connected between one end and the other end of thesecondary winding.

Further, a voltage at the one end of the secondary winding is applied toa negative input terminal of the OP-amp 33 as is, and a voltage at theother end of the secondary winding is applied to a positive inputterminal of the OP-amp 33 via a resistor 37. Slight offset in thenegative polarity is added to the OP-amp 33. As a result, the outputfrom the OP-amp 33 shows the negative polarity when there is nointentional input to the OP-amp 33, thus, the bipolar transistor 11 isprevented from being activated erroneously by noise, or the like.Instead of the resistor 37, a direct current source such as a batterymay be connected so that the negative side of the direct current sourceis connected to the positive input terminal.

An output terminal of the OP-amp 33 is connected to the base B of thebipolar transistor 11 via a current regulating resistor 39.

The emitter E of the bipolar transistor 11 is connected to the groundvoltage terminal GND of the OP-amp 33.

A portion enclosed by a broken line 14 in FIG. 5(A), that is, thebipolar transistor 11, the transformer 31, the OP-amp 33, the diodes 35,and the resisters 37 and 39 form the integrated circuit (IC). This IC 14comprises a source terminal to which the target voltage to be rectifiedis applied, an output terminal to which the rectified voltage isapplied, and two source terminals VDD and VSS of the OP-amp 21.

Operations of the rectification circuits shown in FIGS. 5(A) and (B)will now be described with reference to the timing charts shown in FIGS.6(A) to (C).

First, when the polarity of the source voltage shown in FIG. 6(A)becomes positive, an electric current flows from the emitter E to thecollector C in the circuit shown in FIG. 5(A) because of the forwardconductivity characteristics of the diode 11 b. At that time, thevoltage between the emitter E and the collector C becomes approximately0.6V (when a schottky-barrier diode is used, it becomes approximately0.4V) as shown in FIG. 6(B).

In the circuit shown in FIG. 5(B), a current flows from the emitter E tothe base B.

Because of the current, a voltage is generated also at the secondarywinding of the current transformer 31. The OP-amp 31 amplifies thevoltage and applies a control signal having a positive polarity to thebase B of the bipolar transistor 11. Thus, the bipolar transistor 11 isactivated, and the voltage between the emitter E and the collector Cdrops to approximately 0V, therefore, almost the whole source voltage isapplied to the load 17.

If the source voltage drops and the current gets closer to 0 A, aninductive voltage in the secondary side also drops. Because the OP-amp33 is biased toward the negative polarity side, the OP-amp 33 applies abias signal having a negative polarity to the base B and inactivates thebipolar transistor 11. However, the current flows via the diode 11 b,and a forward voltage for the diode 11 b is applied between the emitterE and the collector C of the bipolar transistor.

When the polarity of the source voltage becomes negative, the bipolartransistor 11 and the diode 11 b become non conductive. Therefore, nocurrent flows through the primary winding of the current transformer 31,and also the secondary winding thereof generates no current. However,because the OP-amp 33 is biased toward the negative side, the OP-amp 33applies a control signal having a negative polarity to the base B of thebipolar transistor 11. Thus, the bipolar transistor is inactivatedcompletely, and the whole of the source voltage is applied between theemitter E and the collector C, and the ground voltage is applied to theload 17.

As described above, the alternating voltage can be rectified by thestructure shown in FIGS. 5(A) and (B). Moreover, because the bipolartransistor 11 is activated in the saturation area, the voltage betweenthe emitter E and the collector C is almost 0V, therefore, rectificationwith almost no loss can be performed.

FIG. 7 shows another example of the rectification circuit.

In this example, the control circuit 13 of the rectification circuit iscomprised of the current transformer 31 and a diode 41 for protection.

The primary winding of the current transformer 31 is provided in thecurrent path extending from the power source 15 to the emitter E of thebipolar transistor 11.

One end of the secondary winding of the current transformer 31 isconnected to the power source 15 so as to show the additive polarity,and the other end of the secondary winding is connected to the base B ofthe bipolar transistor 11. Furthermore, the anode and cathode of thediode 41 are connected to the emitter E and the base B of the bipolartransistor 11, respectively.

An operation of the rectification circuit shown in FIG. 7 will now bedescribed.

When the source voltage is raised and the polarity thereof becomespositive, a current flows from the emitter E to the base B because ofthe forward conductivity characteristics of the diode 41. At that time,the potential difference between the emitter E and the base B becomesapproximately 0.6V (when a schottky-barrier diode is connected, itbecomes approximately 0.4V).

Because of the current, a secondary current, corresponding to the turnratio of the primary winding secondary winding of the currenttransformer 31, occurs and is supplied to the base B. Because of thesecondary current, the voltage for the base B becomes higher than thevoltage for the emitter E, and a reverse voltage is applied to the diode41. Therefore, no current flows through the diode 41. Thus, the bipolartransistor 11 is activated, and the potential difference between theemitter E and the collector C drops to almost 0V, therefore, almost thewhole source voltage is applied to the load 17.

When the source voltage drops and the current gets closer to 0 A, thevoltage in the secondary side of the current transformer 31 also drops.Moreover, counter-electromotive force is generated by the selfinduction. And a forward current flows through the diode 41. Then, areverse bias voltage which is approximately 0.6V (when aschottky-barrier diode is used, it is approximately 0.4V) is appliedbetween the base B and the emitter E.

Therefore, the alternating voltage can be also rectified by thestructure shown in FIG. 7. Moreover, because the current drive abilityof the current transformer 31 is high, an adequate bias current issupplied to the base B of the bipolar transistor 11 to activate thebipolar transistor 11 in the saturation area. Therefore, the voltagebetween the emitter E and the collector C can be reduced to almost 0V,and the rectification with almost no loss can be accomplished.

As shown by a broken line in FIG. 7, the diode 11 b may be connectedbetween the emitter E and the collector C of the bipolar transistor 11so that the direction from the emitter E to the collector C is theforward direction. In this case, when the source voltage raises and thepolarity thereof becomes positive, a current flows via the diode 11 b.The current causes the generation of a secondary current at thesecondary winding of the current transformer 31. The secondary currentis supplied to the base B, and the bipolar transistor 11 is activated.

(Rectification Circuit Using PNP Bipolar Transistor)

In the above described embodiment, although the NPN bipolar transistoris used as a rectification switching element, a PNP bipolar transistormay be used.

FIGS. 8, 9(A), 9(B) and 10 show examples of rectification circuits eachusing a PNP bipolar transistor 51.

The basic structures of these rectification circuits are the same asthose of the rectification circuits shown in FIGS. 4, 5(A), 5(B), and 7.Emitter E of the PNP bipolar transistor 51 is connected to the powersource 15 side, collector C is connected to the load 17, and base B isconnected to the control circuit.

In FIG. 9(A), a diode 11 b or a schottky-barrier diode is connectedbetween the emitter E and the collector C of the bipolar transistor 51so that the direction from the collector C to the emitter E is theforward direction.

In FIG. 9(B), the diode 11 b is connected between the emitter E and thebase B of the bipolar transistor 51 so that the direction from the baseB to the emitter E is the forward direction.

In the examples shown in FIGS. 9(A) and (B), the bipolar transistor 51is inactivated when a control signal having the positive polarity isapplied to the base B. Therefore, a voltage at one end of a secondarywinding is applied to a negative input terminal of an OP-amp 31 as itis, and a voltage at the other end of the secondary winding is appliedto a positive input terminal of the OP-amp 31 via a resistor 37 (some ofoffset voltages of the OP-amp 31 may be set to the positive voltageside).

In the rectification circuit shown in FIG. 10, when the polarity of thesource voltage becomes negative, a current flows from the collector C toa transformer 31 via the base B and a diode 41 in order. The currentcauses the generation of a secondary current at the secondary winding ofthe current transformer 31. The secondary current is supplied to thebase B, thus, the bipolar transistor 51 is activated. The potentialdifference between the emitter E and the collector C drops to almost 0V,and almost the whole source voltage is applied to the load 17.

When the source voltage drops and the current gets closer to 0 A, thevoltage at the secondary side of the current transformer 31 also drops.Moreover, counter-electromotive force is generated by the selfinduction. And a forward current flows through the diode 41. Then, areverse bias voltage is applied between the base B and the emitter E,thus, the bipolar transistor 51 is inactivated.

As shown by a broken line in FIG. 10, the diode 11 b may be connectedbetween the emitter E and the collector C of the bipolar transistor 51so that the direction from the collector C to the emitter E is theforward direction. In this case, when the polarity of the source voltagebecomes negative, a current flows via the diode 11 b. The current causesthe generation of a secondary current at the secondary winding of thecurrent transformer 31. And the secondary current is supplied to thebase B. thus, the bipolar transistor 51 is activated.

Each of the control circuits activates the PNP bipolar transistor 51 inthe saturation area when the polarity of the source voltage is negative(more precisely, when the emitter voltage is lower than the collectorvoltage), and inactivates the PNP bipolar transistor 51 when thepolarity of the source voltage is positive (when the emitter voltage ishigher than the collector voltage).

According to these rectification circuits, the bipolar transistor 51 isactivated when the polarity of the source voltage is negative (when theemitter voltage is lower than the collector voltage), and the voltagebetween the emitter E and the collector C of the bipolar transistor 51drops to almost 0V, and the source voltage is applied to the load 17, asshown in FIG. 11. On the other hand, the bipolar transistor 51 isinactivated when the polarity of the source voltage is positive (whenthe emitter voltage is higher than the collector voltage), and thesource voltage is applied between the emitter E and the collector C ofthe bipolar transistor 51. Then, the ground voltage is applied to theload 17.

(Rectification Circuit Using N-Channel Type FET)

A field effect transistor (FET) may be used as a switching element forrectification.

FIGS. 12, 13 and 14 show examples of the structures of rectificationcircuits each using an N-channel type FET 61.

The basic structures of these rectification circuits are the same asthose of the rectification circuits shown in FIGS. 4, 5 and 7. Source Sof the FET 61 is connected to the power source 15 side, drain D isconnected to the load 17, and gate G is connected to the controlcircuit.

Each of the control circuits activates the FET 61 under the saturationby applying a voltage having the positive polarity to the gate G whenthe polarity of the source voltage is positive (when the source voltageis higher than the drain voltage), and inactivates the FET 61 byapplying a voltage having the negative polarity to the gate G when thepolarity of the source voltage is negative (when the source voltage islower than the drain voltage).

According to these rectification circuits, the FET 61 is activated underthe saturation when the polarity of the source voltage is positive (whenthe source voltage is higher than the drain voltage). Therefore, thevoltage between the source S and the drain D of the FET 61 drops toalmost 0V, and the source voltage is applied to the load 17. On theother hand, the FET 61 is inactivated when the polarity of the sourcevoltage is negative. The source voltage is applied between the source Sand the drain D, and the ground voltage is applied to the load 17.

As describe above, the rectified voltage having the positive polarity isapplied to the load 17.

In the rectification circuits shown in FIGS. 13 and 14, a parasiticdiode of the FET 61 may be used as the diode 11 b.

(Rectification Circuit Using P-Channel Type FET)

A P-channel FET may be used as the switching FET 61. FIGS. 15, 16 and 17show examples of structures of rectification circuits each using theP-channel type FET 61.

Moreover, an arbitrary FET, such as a junction type FET (J-FET), a MOS(Metal-Oxide-Semiconductor) type FET, or a static induction typetransistor (SIT), may be used as a switching FET.

The voltage of the a control signal output from the control circuit canbe selected arbitrarily corresponding to the characteristics of atransistor (a bipolar transistor or an FET) which is being used.

For example, if a normally-on type element, such as a junction type FET,or a depression type MOS, for example, is used as a transistor, anarbitrary voltage (for example, the potential which is equal to thesource potential) for keeping the transistor being activated may beapplied to gate G when the transistor is activated, and an inactivationvoltage may be applied when the transistor is inactivated.

The above indicated values, voltage values, or the like in the abovedescribed embodiments are just examples, therefore, they may be changedarbitrarily. A plurality of diodes may be connected directly when a biasvoltage, a pinch-off voltage, or the like can not be obtained by asingle diode, a Zener diode, a resistor, or the like which is usedsingly.

In the cases of an element such as a MOSFET through which a current,which is large enough to break the element, cannot flow because itsinput impedance is very high, the current regulating resistors 23 and 39or the like are unnecessary.

In FIGS. 5, 7, 9, 10, 13, 14, 16, 17, etc., the transformers, eachhaving the primary winding and the secondary winding, are used as thetransformer 31. However, for example, an auto-transformer 81 or the likemay be used as shown in FIG. 18, as a modification of the rectificationcircuit shown in FIG. 13 or may be used as shown in FIG. 19 as amodification of the rectification circuit shown in FIG. 14. In bothcases where the transformer 31 having the primary and the secondarywindings is used and the case where the auto-transformer 81 is used, aprimary terminal is connected to one end of the transistor, and asecondary terminal is connected to a control terminal.

(Rectification Circuit Whose Collector is Connected to Power SourceSide)

In the rectification circuits shown in FIGS. 4, 5(A), 5(B), 7, 8, 9(A),9(B) and 10, the emitter of the bipolar transistor 11 or 51 is connectedto the power source side, and the collector is connected to the loadside. However, a rectification circuit having such a structure that thecollector of the bipolar transistor 11 or 51 is connected to the powersource side and the emitter is connected to the load side, may beadopted.

For example, the rectification circuit shown in FIG. 4 may be modifiedas shown in FIG. 20, and the rectification circuit shown in FIG. 8 maybe modified as shown in FIG. 21.

In each of the rectification circuits shown in FIGS. 20 and 21, theemitter E of the bipolar transistor 51 or 11 is connected to the load17, and the collector C is connected to the power source 15. An outputterminal of the OP-amp 21 is connected to the base B of the bipolartransistor 51 or 11 via the resistor 23, a positive input terminalthereof is connected to the emitter E of the bipolar transistor 51 or11, and a negative input terminal thereof is connected to the collectorC of the bipolar transistor 51 or 11 via the constant current source 25.And diodes 27 a and 27 b are connected parallel with each other betweenthe positive input terminal and the negative input terminal so that thediodes are opposite in direction from each other. And a ground terminalof the OP-amp 21 is connected to the emitter of the bipolar transistor51 or 11.

Further, in those circuits, the power for the OP-amp 21 is obtained froma rectified current. According to this structure, the operationalvoltage of the OP-amp 21 can be set at a relatively low value,therefore, the source voltage can be reduced.

Similarly, the rectification circuits shown in FIGS. 5(A) and (B) may bemodified as shown in FIGS. 22(A) and (B), and the rectification circuitsshown in FIGS. 9(A) and (B) may be modified as shown in FIGS. 23(A) and(B).

In FIGS. 22(A) and (B), the collector of the PNP type bipolar transistor51 is connected to the power source 15, and the emitter E thereof isconnected to the load 17 via the first winding of the currenttransformer 31.

One end of the secondary winding of the current transformer 31 isconnected to the load 17. The diodes 35 for regulating the voltage areconnected between two ends of the secondary winding.

Further, the voltage at the one end of the secondary winding is appliedto a negative input terminal of the OP-amp 33 as is, and the voltage atthe other end of the secondary winding is applied to a positive inputterminal of the OP-amp 33. An output terminal of the OP-amp 33 isconnected to the base B of the bipolar transistor 11 via the currentregulating resistor 39. The OP-amp 33 is biased toward the positivepolarity.

The emitter E of the bipolar transistor 11 is connected to the groundvoltage terminal GND of the OP-amp 33.

Similarly in these circuits, a rectified voltage is used as theoperational voltage of the OP-amp 33. In such a structure also, theoperational voltage is set at a relatively low value, and the sourcevoltage is reduced.

In the structure shown in FIG. 22(A), the diode 11 b is connectedbetween the emitter and the collector of the bipolar transistor 51. Inthe structure shown in FIG. 22(B), the diode 11 b is connected betweenthe emitter and the base of the bipolar transistor 51.

When the polarity of the voltage from the power source 15 becomesnegative, a current flows via the diode 11 b, the primary winding of thecurrent transformer 31 and the load 17, and a voltage is generated atthe secondary winding. The OP-amp 33 amplifies the generated voltage andapplies a control signal having the positive polarity to the base B ofthe bipolar transistor 51. Thus, the bipolar transistor 51 is activated,the voltage between the emitter E and the collector C drops to almost0V, and almost the whole source voltage is applied to the load 17.

When the source voltage increases and the current gets closer to 0 A,also the inductive voltage on the secondary side reduces. Because theOP-amp 33 is biased toward the positive polarity, the OP-amp 33 appliesa bias signal having the positive polarity to the base B to inactivatethe bipolar transistor 51.

When the polarity of the source voltage becomes to positive, the bipolartransistor 11 and the diode 11 b become non conductive. Thus, no currentflows through the primary winding of the current transformer 31, and nocurrent is generated by the secondary winding thereof. However, becausethe OP-amp 33 is biased toward the positive side, the OP-amp 33 appliesa control signal having the positive polarity to the base B of thebipolar transistor 11. Thus, the bipolar transistor 11 is inactivatedcompletely, the whole of the source voltage is applied between theemitter E and the collector C, and the ground voltage is applied to theload 17.

The structure shown in FIGS. 23 (A) and (B) differs from the structureshown in FIGS. 22 (A) and (B) in that the PNP type bipolar transistor 51is replaced with the NPN bipolar transistor 11, and the OP-amp 33 isbiased toward the negative polarity.

When the polarity of the voltage from the power source 15 becomespositive, a current flows via the diode 11 b, the primary winding of thecurrent transformer 31 and the load 17, and a voltage is generated bythe secondary winding. The OP-amp 33 amplifies the generated voltage,and applies a control signal having the positive polarity to the base Bof the bipolar transistor 51. Thus, the bipolar transistor 51 isactivated, the voltage between the emitter E and the collector C dropsto almost 0V, and almost the whole source voltage is applied to the load17.

When the source voltage increases and the current gets closer to 0A, aninductive voltage on the secondary side also drops. Because the OP-amp33 is biased toward the negative polarity, the OP-amp 33 applies a biassignal having the negative polarity to the base B, and inactivates thebipolar transistor 51.

When the polarity of the source voltage becomes negative, the bipolartransistor 11 and the diode 11 b become non conductive. Thus, no currentflows through the primary winding of the current transformer 31, andalso no current is generated by the secondary winding thereof. However,because the OP-amp 33 is biased toward the negative polarity, the OP-amp33 applies a control signal having the negative polarity to the base Bof the bipolar transistor 11. Thus, the bipolar transistor 11 isinactivated completely, the whole of the source voltage is appliedbetween the emitter E and the collector C, and a ground voltage isapplied to the load 17.

As described above, an alternating voltage can be rectified by thestructures shown in FIGS. 22(A), (B), and 23(A), (B). Moreover, becausethe bipolar transistor 11 is activated in the saturation area, thevoltage between the emitter E and the collector C is almost 0V, thus,the rectification with almost no loss can be accomplished.

Similarly, the rectification circuit shown in FIG. 7 may be modified asshown in FIG. 24, and the rectification circuit shown in FIG. 10 may bemodified as shown in FIG. 25.

Moreover, the rectification circuit shown in FIG. 12 may be modified asshown in FIG. 26, and the rectification circuit shown in FIG. 15 may bemodified as shown in FIG. 27.

Furthermore, the rectification circuit shown in FIG. 13 may be modifiedas shown in FIG. 28, and the rectification circuit shown in FIG. 16 maybe modified as shown in FIG. 29.

In each of these rectification circuits, because a control section forswitching the transistor is disposed on the ground side (load side), novoltage is applied to the control section when a reverse voltage isapplied, therefore, it is safe. Also, the source voltage can be reduced.

And, it is efficient because the operational voltages of the OP-amps 21and 33 are obtained from the rectified voltage.

The diode 11 b may be removed.

FIG. 32 shows another example of the rectification circuit of thepresent invention.

In a rectification circuit 100 shown in FIG. 32, a field effecttransistor 110 is, for example, an N-channel type MOS-FET, and thesource thereof is connected to a secondary coil of a transformer 112,and drain terminal D is connected to a load 113.

A branch line extending from source terminal S of the FET 110 and apower supplying line whose potential is 0 are connected to a positiveinput terminal of an OP-amp 111 which is one of the components forming acontrol circuit, and a branch line extending from the drain terminal Dis connected to a negative input terminal of the OP-amp 11 via aresistor Ra. A diode Dr is connected between the input terminals tohinder a sneak current. A potential dividing resistor Rc is connectedbetween the power supplying line of a positive bias potential (Vcc) andthe negative input terminal (−) of the OP-amp 111. The output from theOP-amp 111 is input to gate G of the FET 110 via a resistor Rb. It ispreferred that, for example, the resistors Ra, Rb and Rc beapproximately 10 kΩ, 2 MΩ and 180Ω, respectively. The resistor Rb isused for adjusting the potential, however, it may be removed when an FETis used. In a practical usage, for example, a capacitor having apredetermined capacity is connected parallel to the load 113.

Also in the circuit shown in FIG. 32, a balance is maintained betweenthe positive and negative input terminals of the OP-amp 111 when thealternating power is not input to the FET 110. Therefore, the potentialof the output Sb from the OP-amp 111 becomes 0. Under this condition,let it be supposed that a sine wave alternating voltage Sa is input tothe FET 110 from the transformer 112 as shown in FIG. 33 (A). In the FET110, the potential at the source terminal S becomes very higher than thepotential at the drain terminal D when the polarity of the alternatingvoltage Sa is positive. At that moment, the OP-amp 111 detects that thepotential difference occurs based on the potential difference betweenthe positive and negative input terminals, and change the outputpotential Sb to a positive bias potential (Vcc). Meanwhile, because thepotential at the source terminal S becomes lower than the potential forthe drain terminal D at the time that the polarity of the alternatingvoltage Sa changes to negative from positive, the OP-amp 111 detectsthis change, and changes the output voltage Sb to a negative biaspotential (−Vcc) immediately. The waveform shown in FIG. 33 (B) showschanges in the potential of the output Sb from the OP-amp 111.

When the polarity of the output voltage Sb from the OP-amp 111 ispositive, the FET 110 is turned on, therefore, a current flows from thesource terminal S to the drain terminal D. On the other hand, when theoutput voltage Sb from the OP-amp 111 has a negative bias potential, theFET 110 is turned off, therefore, the current is cut off. As a result,the voltage (rectified voltage) Sc to be applied to the load 113 becomesa pulsating voltage from which only the negative polarity components ofsine waves have been removed as shown in FIG. 33 (C).

Such a mode of supplying power to the source terminal S and the drainterminal D, is opposite to the original power supplying mode of the FET.However the present invention adopts the above described power supplyingmode in order to positively use following points: the back withstandingvoltage, that is, the potential difference between the gate and thedrain when the current is cut off, can be made to be very high becausethe above potential difference is one which the FET inherently has;resistor components in the forward direction are extremely low andstable; the back recovery time is short; and the amount of leakagecurrent is small. In an experiment, a back withstanding voltage ofapproximately 1000 [V] was attained even though a general-purpose FETwas used.

A P-channel type FET may be used instead of the N-channel type FET. Inthis case, the P-channel type FET operates in the same manner as theN-channel type FET, but the direction of the current is different. Evenif a junction type FET (J-FET) or a bipolar transistor is used, anoperation is performed in almost the same manner, expect that a drop inthe voltage between an input terminal and an output terminal of thetransistor is slightly different.

As described above, using the rectification circuit of the presentinvention, a drop in the voltage in the forward direction can be reducedover that of a conventional apparatus. It means that the loss of poweroccurring during the rectification and heat irradiation from the insideof the element due to the power loss are extremely reduced. Moreover,the structure of the apparatus can be simplified and miniaturizedbecause a cooling device is unnecessary.

Furthermore, the rectified voltage can be used as a power for theOP-amp.

For example, when the load 17 in the rectification circuit shown in FIG.4 includes a battery as shown in FIG. 34, an OP-amp 21 may be driven bysupplying a rectified voltage of the positive polarity to the sourceterminal of the OP-amp 21.

Similarly, if the load 17 in the rectification circuit shown in FIG. 4includes a capacitor, the OP-amp 21 may be driven by supplying arectified voltage of the positive polarity to the source terminal of theOP-amp 21, as shown in FIG. 35. In this rectification circuit, anexternal diode 11 b (which may be a parasitic diode when the transistoris an FET) causes a rectification current to flow first, and then avoltage is generated at the load 17. The voltage activates the OP-amp21, and the transistor 51 operates as a diode.

When the load 17 is not a resistor or the like having no voltage, therectified voltage may be used as the operational voltage of the OP-ampas shown in FIG. 36. In this case also, a rectified current flows firstdue to the presence of the external diode 11 b, and then a voltage isgenerated in the load 17. The voltage activates the OP-amp 21, and thetransistor 51 is activated as a diode.

Moreover, when the load 17 is not a resistor or the like having novoltage, a rectification circuit may be comprised of simple circuits asshown in FIGS. 37 and 38.

In the structure shown in FIG. 37, the collector C of the PNP bipolartransistor 51 is connected to the output by the power source 15, thebase B is grounded via the resistor 31 for regulating (limiting) acurrent value, and the emitter E is connected to the load 17.

In this structure, when the polarity of the output from the power source15 is positive, a base current flows from the collector C of the PNPbipolar transistor 51 to the resistor 31 via the base B. The basecurrent causes a collector current, that is, a load current to flow fromthe collector C to the load 17 via the emitter E.

On the other hand, when the polarity of the output from the power source15 is negative, no base current flows because the voltage between thecollector C and the base B of the PNP bipolar transistor 51 is a counterbias voltage. Therefore, no current flows from the emitter E to thecollector C.

A diode may be connected between the base B and the emitter E so thatthe direction from the base B to the emitter E is the forward direction.In this case, a current flows through the diode until the base currentflows through the resistor 31.

In the structure shown in FIG. 38, drain D of a P-channel FET 71 isconnected to the output of the power source 15, gate G is grounded viathe resistor 31 for regulating (limiting) current, and source S isconnected to the load 17. Further, a Zener diode 41 for protecting thegate is connected between the gate G and the source S so that thedirection from the gate G to the source S is the forward direction.

In this structure, when the polarity of the output from the power source15 is positive, a parasitic diode causes a current to flow from thedrain D of the FET 71 to the load 17 via the source S, and a voltagewhose polarity is positive is applied to the load 17. If the polarity ofthe voltage applied to the load 17 becomes positive, a voltage for thegate G becomes a negative voltage relatively, and the FET 71 isactivated.

On the other hand, when the polarity of the output from the power source15 is negative, no current flows through the parasitic diode, and alsono bias voltage is not applied to the gate G. Therefore, the FET 71 isinactivated.

(Switching Power Source)

An embodiment in which the rectification circuit of the presentinvention is applied to a switching (SW) power source will now bedescribed. FIG. 39 is a block diagram showing the SW power source inthis embodiment.

As shown in FIG. 39, the SW power source 202 comprises a transformer 115for outputting an alternating voltage showing a rectangular waveform,and an active semiconductor element, for example, a MOS-type-FET 220,for rectifying the alternating voltage obtained from the transformer215. Two taps for outputting voltages having the same alternating cyclebut different amplitude values are arranged on a secondary coil of thetransformer 215. A first tap for outputting a voltage having a smallamplitude value is connected to source terminal S of the FET 220, and asecond tap for outputting a voltage having a large amplitude value isconnected to gate terminal G of the FET 220. A load and a capacitor, forexample, an electrolytic capacitor C, are connected parallel to drainterminal D of the FET 220 via a smoothing coil L.

In the SW power source 220 having such components, let it be supposedthat an alternating signal Sd, showing a rectangular waveform, whosealternating cycle is 200 [kHz], amplitude value is ±5 [V], and currentvalue is 10 [A] for example, is applied to the source terminal S of theFET 220 from the first tap of the transformer 215, and an alternatingvoltage whose amplitude value is ±12 [V] is applied to the gate terminalG of the FET 220 from the second tap, as shown in FIG. 40 (A). In thiscase, when the polarity of the alternating voltage Sd is positive, theamplitude value of the power at the gate terminal G (12 [V]) becomesrelatively larger than the amplitude value of the power at the sourceterminal S (5 [V]), thus, the FET 220 is activated. That is, a portionbetween the source terminal S and the drain terminal D conductive,therefore, a current flows from the source terminal S to the drainterminal D.

On the other hand, when the polarity of the alternating voltage Sd isnegative, because the amplitude value of the power at the gate terminalG (−12 [V]) becomes lower than the amplitude value of the power at thesource terminal S (−5 [V]), the FET 220 is inactivated, thus, thecurrent is cut off. Therefore, positive polarity components Se of thealternating voltage Sd is output from the FET 220 and are rectified. (Ofthe positive polarity components Se, those whose frequency is equal toor greater than the frequency determined by the smoothing coil L and thecapacitor C are inhibited from passing, and therefore the raising andfalling of the output of the positive polarity components Se are, inactual fact, not completed instantly, but change exponentially.)

Almost no drop occurs in the voltage in the forward direction during therectification, as well as in the case described above. And a leakagecurrent is negligibly little when the power is supplied in the reversedirection, thus, the voltage can be rectified efficiently because of areduction in the loss of power. Actually, even if a rectifying operationis performed for several hours continuously, the FET 220 does notirradiate heat, and the inventor of the present invention has confirmedthat a heat sink plate or the like was unnecessary. Moreover, a controlcircuit is unnecessary because the alternating voltage Sd has arectangular waveform, and the time required for changing the polarityfrom positive to negative, or from negative to positive is short. Thevoltage distribution to the FET 220 when the power is supplied in thereverse direction corresponds to the original voltage distribution in anormal usage, that is, a voltage Vds between the drain and the source.Thus, a high withstanding ability can also be obtained.

If a bipolar transistor or a J-FET is used instead of the MOSFET, almostthe same operation as that described above is performed. In this case,however, an element for regulating the current, such as a resistorelement, for example, is inserted between the gate terminal and thesecond tap of the transformer 215.

FIG. 41 shows another example of the switching power source 202according to the embodiment of the present invention. This rectificationcircuit comprises the transformer 215, the FET 220, a bipolar transistor204, a diode 205, base resistor 206, a bias resistor 207, and an outputterminal 208.

As shown in FIG. 42, the transformer 2 comprises a primary winding Ta, asecondary winding Tb, a detection winding Tc, and an iron core Td. Theprimary winding Ta is wound around one of opposing legs of the iron coreTd which is a rectangular, and the secondary winding Tb is wound aroundthe other leg thereof. The detection winding Tc is wound around the sameleg on which the primary winding is wound, and the number of turns ofthe detection winding is the same as that of the secondary winding Tb.

The voltage between both electrodes of an external alternating powersource 1 is applied to both ends of the primary winding Ta. The drain ofthe FET 220 and a hot end of the detection winding Tc are connected to ahot end of the secondary winding Tb. A cold end of the secondary windingTb is connected to a positive electrode of the output terminal 208, andis connected to base B of the bipolar transistor 204 via the baseresistor 206 which is equipped for regulating the base current. A coldend of the detection winding Tc is connected to emitter E of the bipolartransistor 204.

The FET 220 is an n-channel enhancement type MOS(Metal-Oxide-Semiconductor) FET. The drain D of the FET 220 is connectedto the hot end of the secondary winding Tb and that of the detectionwinding Tc of the transformer 215. Source S is connected to a negativeelectrode of the output terminal 208. Gate G is connected to collector Cof the bipolar transistor 204.

The bias resistor 207 is connected between the gate G and the source Sof the FET 220.

A diode is connected between the source S and the drain D of the FET 220so that the direction from the source S to the drain D is the forwarddirection. An independent diode or the parasitic diode of the FET 220may be used as the above-mentioned diode.

The bipolar transistor 204 is a PNP type. The collector C of the bipolartransistor 204 is connected to the gate G of the FET 220, the emitter Eis connected to the cold end of the detection winding Tc, and the base Bis connected to the cold end of the secondary winding Tb of thetransformer 2 via the base resistor 206.

The diode 205, for preventing a reverse bias from being applied betweenthe base B and the emitter E of the bipolar transistor, is connectedbetween the base B and the emitter E of the bipolar transistor 204 sothat the direction from the base B to the emitter E is the forwarddirection.

An operation when a load 217 is connected between electrodes of theoutput terminal 208 in the rectification circuit shown in FIG. 41 willnow be described with reference to the timing charts shown in FIGS.43(A) to (E).

FIG. 43(A) shows the waveform of the source voltage output from thealternating current source 15, FIG. 43(B) shows the waveform of the gatevoltage to be applied to the FET 220, FIG. 43(C) shows the turning onand off of the FET 220, FIG. 43(D) shows the waveform of the voltage tobe applied between the drain D and the source S of the FET 220, and FIG.43(E) shows the waveform of the voltage to be applied to the load 217.

First, when the polarity of the source voltage shown in FIG. 43(A)becomes negative (in other words, the voltage at the hot end of theprimary winding Ta becomes lower than that at the cold end thereof), thesecondary winding Tb and the detection winding Tc generate a secondaryvoltage so that the voltage at the hot end becomes lower than that atthe cold end.

At that time, the voltages generated at both ends of the secondarywinding Tb are supplied to the load via the diode connected between thesource S and the drain D of the FET 220. A load current flows throughthe secondary winding because of power consumption at the load, andthen, the voltage between the ends of the secondary winding Tb drops dueto the internal resistance of the secondary winding Tb and the magneticresistance caused by the transformer 215.

On the other hand, the detection winding Tc does not allow a current toflow when the bipolar transistor 204 is inactivated. Even if the bipolartransistor 204 is activated, the detection winding Tc does not apply avoltage to the load 217.

Because of this, the extent of a drop, which occurs in the voltagebetween the terminals of the detection winding Tc, is smaller than thatof the voltage between the terminals of the secondary winding Tb if theimpedance of a section to which the both ends of the detection windingTc are connected is satisfactorily higher than the impedance of the load217.

As a result, the voltage at the cold end of the secondary winding Tbbecomes lower than the voltage at the cold end of the detection windingTc, and the potential difference between the both cold ends becomesalmost equal to a difference between the quantity of the voltage betweenthe both ends of the secondary winding Tb and the quantity of thevoltage between the both ends of the detection winding Tc.

Then, the voltage between the both cold ends is applied between the baseB and the emitter E of the bipolar transistor 204. As a result, thebipolar transistor 204 is activated when the voltage at the base B ofthe bipolar transistor 204 becomes lower than the voltage at the emitterE by approximately 0.6 V or greater.

After the bipolar transistor 204 is activated, a current path is formedextending from the cold end of the detection winding Tc to the hot endof the detection winding Tc via the emitter E and the collector C of thebipolar transistor 204, the bias resistor 207, and the source S and thedrain D of the FET 220 in order.

As a result, the voltage drop shown in FIG. 43(B) occurs at the bothends of the bias resistor 207, and the voltage at the gate G of the FET220 becomes higher than the voltage at the source S. Therefore, the FET220 is forward biased, and the FET 220 is saturated as shown in FIG.43(C).

Under the saturation, the voltage between the source S and the drain Dof the FET 220 is almost 0 (being shunt), and the voltages at the sourceS and drain D are almost the same as each other. Further, the voltage isvery lower than the forward voltage in the diode.

Because of this, almost no voltage drop occurs at the FET 220 as shownin FIG. 43(D), and the voltage which is almost equal to the sourcevoltage is applied to the load 217 as shown in FIG. 43(E).

Then, when the polarity of the source voltage shown in FIG. 43(A)becomes positive, the secondary winding Tb and the detection winding Tcgenerate a secondary voltage so that the voltage at the hot end becomeshigher than that at the cold end.

At that time, if a load current flows through the secondary winding Tb,the voltage between the both ends of the secondary winding Tb dropsbecause of the internal resistance of the secondary winding Tb and themagnetic resistance of the transformer 215. On the other hand, thedetection winding Tc generates a voltage whose quantity is proportionalto the impedance of a section where the both ends of the detectionwinding Tc are connected.

As a result, when the impedance of the section where the both ends ofthe detection winding Tc are connected is satisfactorily higher than theimpedance of the load 217, the voltage at the cold end of the secondarywinding Tb becomes higher than the voltage at the cold end of thedetection winding Tc. In this case, the potential difference between theboth cold ends is also almost equal to the difference between thequantity of the voltage between the both ends of the secondary windingTb and the quantity of the voltage between the both ends of thedetection winding Tc.

The voltage between the both ends is applied between the base B andemitter E of the bipolar transistor 204, and the voltage at the base Bof the bipolar transistor 204 becomes higher than the voltage at theemitter E. As a result, the bipolar transistor 204 is inactivated.

After the bipolar transistor 204 is inactivated, the current path,extending from the cold end of the detection winding Tc to the hot endof the detection winding Tc via the emitter E and collector C of thebipolar transistor 204, the bias resistor 207 and the source S and drainD of the FET 220 in order, is cut off.

Then, no bias voltage is applied between the gate G and source S of theFET 220 (in other words, the potentials at the gate G and the source Sbecome almost the same as each other). Because the FET 220 is theenhancement type FET, the FET 220 is reversely biased, thus, the FET 220is inactivated as shown in FIG. 45(C).

As a result, a ground voltage is applied to the load 217 as shown inFIG. 43(E), and a source voltage is applied between the source S and thedrain D (FIG. 43(E) shows the voltage at the drain D whose referencevoltage is the voltage at the source S).

After such processing is repeated, a half-wave rectified voltage whichis applied to the load 217 as shown in FIG. 43(E).

According to the structure shown in FIG. 41, a drop in the voltagebetween the source S and the drain D becomes almost 0 (for example,approximately 5 mV to 40 mV) when the FET 220 is activated. Thus, thealternating voltage can be rectified with a small loss.

Moreover, because the FET 220 is switched off at the time the targetvoltage to be rectified is almost 0, the overshoot and the undershoot donot occur on the rectified voltage.

The waveform of the target voltage to be rectified is not limited to asine wave voltage such as that shown in FIG. 43(A). It may have atriangular waveform, a rectangular waveform, or the like. The voltagewhose average value is not become 0, in other words, the voltagecontaining AC components to which DC components have been added, may berectified.

The transformer 215 is not limited to the above described one. Forexample, the transformer 215 may comprise a power source transformer 215a and a current detecting insulation transformer 215 b.

In this case, a primary winding of the power source transformer 215 aand a primary winding of the insulation transformer 216 b are connectedparallel with each other as illustrated, and an output voltage from thealternating current source 15 is input to their common ends.

A hot end and a cold end of a secondary winding of the power sourcetransformer 215 a are connected to the drain of the FET 220 and one endof the base resistor 206, as well as in the aforementioned case of thehot end and the cold end of the secondary winding Tb of the transformer2.

A hot end and cold end of a secondary winding of the insulationtransformer 215 b are connected to the drain of the FET 222 and theemitter of the bipolar transistor 204, as well as in the aforementionedcase of the hot end and cold end of the detection winding Tc of thetransformer 2.

Moreover, instead of the voltage at collector C of the bipolartransistor 204, a voltage which is obtained by adding a predeterminedbias voltage to the voltage for the collector C may be applied to thegate G of the FET 220. At that time, the FET 220 is not limited to theenhancement type MOSFET. The FET 220 may be a depression type MOSFET, ajunction type FET, or a static induction transistor (SIT).

The rectification circuit may comprise an NPN type bipolar transistor220 b instead of the FET 220.

In this rectification circuit, the base, collector or emitter of thebipolar transistor 220 b is connected to a portion to which the gate G,drain D or source S of the FET 220 should be connected, as shown in FIG.45.

Base resistor 210 for regulating the base current for the bipolartransistor 220 b is connected between the base B of the bipolartransistor 220 b and the collector C of the bipolar transistor 204.

If the NPN type bipolar transistor 220 b is used instead of the FET 220as described above, a bias resistor 207 is connected between the emitterE and the base B of the bipolar transistor 220 b.

In this case, when the polarity of a primary voltage becomes negative,an initial bias current flows via the collector C, the base B and thebias resistor 207 even if a diode does not exist between the collector Cand emitter E, and the bipolar transistor 220 b is activated. As aresult, a current flows through the load 217 and the secondary windingTb, and the voltage appearing between the both ends of the secondarywinding Tb drops. Therefore, the diode between the collector C and theemitter E is unnecessary in this case.

However, a diode may be connected between the collector C and theemitter E so that the direction from the emitter E to the collector C isthe forward direction, for the sake of, for example, adjusting theextent of a drop in the voltage, appearing between the both ends of thesecondary winding Tb to a desired extent.

The rectification circuit may comprise, for example, an FET 204 b whichis a p-channel or enhancement type MOSFET, instead of the bipolartransistor 204.

If the FET 204 b is used, the gate, drain or source of the FET 204 b isconnected to that portion of this rectification circuit to which thebase B, collector C or emitter E of the bipolar transistor 204 should beconnected, as shown in FIGS. 46(A) and (B).

In this case, the base resistor 206 may be removed. If the base resistor206 is removed, the cold end of the secondary winding Tb and the gate ofthe of the FET 204 b may be connected directly.

In this case, a voltage which is obtained by adding a predetermined biasvoltage to the voltage for the cold end of the secondary winding Tb maybe applied to the FET 204 b, instead of the voltage for the cold end ofthe secondary winging Tb.

In this case, the FET 204 b is not limited to the enhancement typeMOSFET. It may be a depression type MOSFET, a JFET (junction type FET),or an SIT.

The operation by which each of the rectification circuits shown in FIGS.45, 46(A), and 46(B) drives the load 217 is substantially the same asthe operation of the rectification circuit shown in FIG. 1.

That is, when the polarity of the source voltage becomes negative, thevoltage at the cold end of the secondary winding Tb becomes lower thanthe voltage at the cold end of the detection winding Tc. Thus, thepotential difference between the both cold ends becomes almost equal tothe difference between the quantity of the voltage between the both endsof the secondary winding Tb and the quantity of the voltage between theboth ends of the detection winding Tc.

As a result, if the voltage at the base B of the bipolar transistor 204becomes lower than the voltage at the emitter E by approximately 0.6V orgreater, or if the voltage at the gate of the FET 204 b becomes lowerthan a pinch-off voltage, the bipolar transistor 204 or the FET 204 b isactivated. A drop occurs in the voltage between the both ends of thebias resistor 207, and the FET 220 or the bipolar transistor 203 b issaturated while being forwardly biased. At that time, a voltage which isalmost equal to the source voltage is applied to the load 217.

Then, when the polarity of the source voltage becomes positive, thevoltage at the cold end of the secondary winding Tb becomes higher thanthe voltage at the cold end of the detection winding Tc, and thepotential difference between the both cold ends becomes almost equal tothe difference between the quantity of the voltage between the both endsof the secondary winding Tb and the quantity of the voltage between theboth ends of the detection winding Tc.

If the voltage at the base B of the bipolar transistor 204 becomeshigher than the voltage at the emitter E, or if the gate voltage of theFET 204 b becomes higher than the pinch-off voltage, the bipolartransistor 204 or FET 204 b is inactivated. As a result, the FET 220 orthe bipolar transistor 220 b is reversely biased and inactivated. Atthat time, a ground voltage is applied to the load 217.

After such processing is repeated, a half-wave rectified voltage isapplied to the load 217.

The FET 220 or the bipolar transistor 220 b may be connected as shown inFIGS. 47(A), (B), 48(A) and (B), for example.

That is, the drain D of the FET 220 or the collector C of the bipolartransistor 220 b may be connected to the negative electrode of theoutput terminal, and the source S of the FET 220 or the emitter E of thebipolar transistor 220 b may be connected to the hot end of thesecondary winding Tb.

Also in each of the rectification circuits shown in FIGS. 47(A), (B),48(A), and (B), when the polarity of the source voltage becomesnegative, the voltage at the cold end of the secondary winding Tbbecomes lower than the voltage at the cold end of the detection windingTc. As a result, if the voltage at the base B of the bipolar transistor204 becomes lower than the voltage at the emitter E by approximately0.6V or greater, or if the voltage at the gate of the FET 204 b becomeslower than the pinch-off voltage, the bipolar transistor or the FET 204b is activated.

At that time, in each of the rectification circuits, a current path isformed extending from the cold end of the detection winding Tc to thehot end of the detection winding Tc via the emitter E and collector C ofthe bipolar transistor 204 (or the source S and drain D of the FET 204b), and bias resistor 207 in order.

Because of this, a drop occurs in the voltage between the both ends ofthe bias resistor 207, the FET 220 or the bipolar transistor 220 b issaturated while being forwardly biased, and a voltage which is almostequal to the source voltage is applied to the load 217.

If the polarity of the source voltage becomes positive and the voltageat the cold end of the secondary winding Tb becomes higher than thevoltage at the cold end of the detection winding Tc, the bipolartransistor 204 or the FET 204 b is reversely biased and inactivated.

At that time, the above mentioned current path, extending from the coldend of the detection winding Tc to the hot end of the detection windingTc via the emitter E and collector C of the bipolar transistor 204 (orthe source S and drain D of the FET 204 b) and bias resistor 207 inorder, is cut off, and substantially no drop occurs in the voltagebetween the both ends of the bias resistor 207.

As a result, the FET 220 or the bipolar transistor 220 b is reverselybiased and inactivated, and then a ground voltage is applied to the load217.

After such processing is repeated, a half-wave rectified voltage isapplied to the load 217.

Further, each of the rectification circuits may comprise a p-channeltype MOSFET and an NPN type bipolar transistor.

FIG. 49 shows a rectification circuit comprising the p-channel typeMOSFET and the NPN type bipolar transistor. As illustrated, the basicstructure of this rectification circuit is the same as that of therectification circuit shown in FIG. 41. However, the FET 220 is thep-channel type MOSFET, and the bipolar transistor 204 is the NPN typebipolar transistor. The cold end of the secondary winding Tb isconnected to the negative electrode of the output terminal 208, and thesource S of the FET 220 is connected to the positive electrode of theoutput terminal 208.

In the case where the FET 220 is the p-channel type MOSFET, a diode isconnected between the source S and the drain D of the FET 220 so thatthe direction from the drain D to the source S is the forward direction.This diode may be an independently prepared diode, or the parasiticdiode of the FET 220.

When the load 217 is connected to the both electrodes of the outputterminal 208 in the rectification circuit shown in FIG. 49, the load 217is driven as described below.

First, when the polarity of the source voltage becomes positive, thesecondary winding Tb and the detection winding Tc generate a secondaryvoltage in such a direction that the voltage for a hot end is higherthan that at a cold end.

At that time, the voltage appearing between the both ends of thesecondary winding Tb is applied to the load via the diode connectedbetween the source S and the drain D of the FET 220. When powerconsumption at the load causes a load current to flow through thesecondary winding Tb, the voltage between the both ends of the secondarywinding is lowered by the resistance of the secondary winding Tb and themagnetic resistance of the transformer 215. On the other hand, a voltagewhose quantity is proportional to the impedance of a section to whichthe both ends of the detection winding Tc are connected, is generatedbetween the both ends of the detection winding Tc.

As a result, when the impedance of the section to which the both ends ofthe detection winding Tc are connected is satisfactorily higher than theimpedance of the load 217, the voltage at the cold end of the secondarywinding Tb becomes higher than the voltage at the cold end of thedetection winding Tc. And the potential difference between the both coldends becomes almost equal to the difference between the quantity of thevoltage between the both ends of the secondary winding Tb and thequantity of the voltage between the detection winding Tc.

Then, the voltage between the both cold ends is applied between the baseB and the emitter E of the bipolar transistor 204. As a result, if thevoltage at the base B of the bipolar transistor 204 becomes higher thanthe voltage at the emitter E by approximately 0.6V or greater, thebipolar transistor 204 is activated.

After the bipolar transistor 204 is activated, a current path is formedextending from the hot end of the detection winding Tc to the cold endof the detection winding Tc via the drain D and source S of the bipolartransistor 204, a bias resistor 207, and the collector C and emitter Eof the bipolar transistor 204 in order.

As a result, a drop occurs in the voltage appearing between the bothends of the bias resistor 207, and the voltage at the gate G of the FET220 becomes lower than that at the source S. Therefore, the FET 220 isforwardly biased, and therefore is saturated.

As a result, the voltage between the source S and the drain D of the FET220 becomes almost 0, and then a voltage which is almost equal to thesource voltage is applied to the load 217.

When the polarity of the source voltage becomes negative, the secondarywinding Tb and the detection winding Tc generate a secondary voltage insuch a direction that the voltage at the hot end is lower than thevoltage at the cold end.

Under this condition, if a load current flows through the secondarywinding Tb, the voltage between the both ends of the secondary windingTb drops because of the resistance of the secondary winding Tb and themagnetic resistance of the transformer 215. On the other hand, a voltagewhose value is proportional to the impedance of a section to which theboth ends of the detection winding Tc are connected, is generatedbetween the both ends of the detection winding Tc.

As a result, if the impedance of the section to which the both ends ofthe detection winding Tc are connected is satisfactorily higher than theimpedance of the load 217, the voltage at the cold end of the secondarywinding Tb becomes lower than the voltage at the cold end of thedetection winding Tc. In this case, the potential difference between theboth cold ends also becomes almost equal to the difference between thequantity of the voltage between the both ends of the secondary windingTb and quantity of the voltage between the both ends of the detectionwinding Tc.

Then, the voltage between the both cold ends is applied between the baseB and the emitter E of the bipolar transistor 204, and the voltage atthe base B becomes lower than the voltage at the emitter, and thebipolar transistor 204 is inactivated.

As a result, potentials at the gate G and the source S of the FET 220are almost equalized. Because the FET 220 is the enhancement type FET,the FET 220 is reversely biased and inactivated. Then the ground voltageis applied to the load 217, and the source voltage is applied betweenthe source S and the drain D.

After such processing is repeated, a half-wave rectified voltage isapplied to the load 217.

Instead of the voltage at the collector C of the bipolar transistor 204,a voltage which is obtained by adding a predetermined bias voltage tothe voltage at the collector C may be applied to the gate G of the FET220. Under this condition, the FET 220 is not limited to the enhancementtype MOSFET. It may be a depression type MOSFET, a junction type FET, oran SIT.

Instead of the FET 220, the PNP type bipolar transistor 220 b may beused in the rectification circuit.

In this case, the base, collector, or emitter of the bipolar transistor220 b is connected to that portion of the rectification circuit to whichthe gate G, drain D or source S of the FET 220 should be connected, asshown in FIG. 50.

The base resistor 210 for regulating the base current for the bipolartransistor 220 b is connected between the base B of the bipolartransistor 220 b and the collector C of the bipolar transistor 204.

In this case, when the polarity of a primary voltage becomes positive,an initial bias current flows via the collector C, the base B and a biasresistor 207 even if a diode does not exist between the collector C andthe emitter E, thus, the bipolar transistor 220 b is activated. As aresult, a current flows through the load 217 and the secondary windingTb, and the voltage between both ends of the secondary winding Tb drops.Therefore, the diode between the collector C and the emitter E isunnecessary in this case.

However, a diode may be connected between the collector C and theemitter E so that the direction from the emitter E to the collector C isthe counter direction, for the sake of adjusting the extent of thevoltage drop at the both ends of the secondary winding Tb to apredetermined extent.

Instead of the bipolar transistor 204, for example, an FET 204 b, whosetype is p-channel type, enhancement type, or MOS type, may be used forthe rectification circuit.

In this case, the gate, drain or source of the FET 204 b is connected tothat portion of the rectification circuit to which the base B, collectorC or emitter E of the bipolar transistor 204 should be connected, asshown in FIGS. 51(A) and (B).

Moreover, the base resistor 206 may be removed in this case, and thecold end of the secondary winding Tb and the gate of the FET 204 b maybe connected directly.

Instead of the voltage for the cold end of the secondary winding Tb, avoltage which is obtained by adding a predetermined bias voltage to thevoltage for the cold end of the secondary winding Tb, may be applied tothe FET 204 b. Under this condition, the FET 204 b is not limited to theenhancement type MOSFET. It may be a depression type MOSFET, a junctiontype FET, or an SIT.

The operation by which each of the rectification circuits shown in FIGS.50, 51(A), and (B) drives the load 217 is the same as the operation ofthe rectification circuit shown in FIG. 48.

That is, if the polarity of the source voltage becomes positive, thevoltage at the cold end of the secondary winding Tb becomes higher thanthe voltage at the cold end of the detection winding Tc, thus, thepotential difference between the both cold ends becomes almost equal tothe difference between the quantity of the voltage between the both endsof the secondary winding Tb and the quantity of the voltage between theboth ends of the detection winding Tc.

As a result, if the voltage at the base B of the bipolar transistor 204becomes higher than the voltage at the emitter E by approximately 0.6Vor greater, or if the voltage at the gate of the FET 204 b becomeshigher than the pinch-off voltage, the bipolar transistor 204 or the FET204 b is activated. Then the voltage drop occurs at the both ends of thebias resistor 207, therefore, the FET 220 or the bipolar transistor 220b is forwardly biased and saturated. At that time, voltage which isalmost equal to the source voltage is applied to the load 217.

Then, if the polarity of the source voltage becomes negative, thevoltage at the cold end of the secondary winding Tb becomes lower thanthe voltage at the cold end of the detection winding Tc, thus, thepotential difference between the both cold ends becomes almost equal tothe difference between the quantity of the voltage between the both endsof the secondary winding Tb and the quantity of the voltage between theboth ends of the detection winding Tc.

If the voltage at the base B of the bipolar transistor 204 becomes lowerthan the voltage at the emitter E of the FET 204 b, or if the gatevoltage of the FET 204 b becomes lower than the pinch-off voltage, thebipolar transistor 204 or the FET 204 b is inactivated. As a result, theFET 203 or the bipolar transistor 203 b is reversely biased andinactivated. At that time, the ground voltage is applied to the load217.

After such processing is repeated, a half-wave rectified voltage isapplied to the load 217.

The form of the connection between the FET 220 or the bipolar transistor220 b and the other devices is not limited to the above described one.They may be connected as shown in, for example, FIGS. 52(A), (B), 53(A),and (B).

That is, the drain D of the FET 220 or the collector C of the bipolartransistor 220 b may be connected to the positive electrode of theoutput terminal, and the source S of the FET 220 or the emitter E of thebipolar transistor 220 b may be connected to the hot end of thesecondary winding Tb.

In each of the rectification circuits shown in FIGS. 52(A), (B), 53(A),and (B), if the polarity of the source voltage becomes positive, thevoltage at the cold end of the secondary winding Tb also becomes higherthan the voltage at the cold end of the detection winding Tc. As aresult, if the voltage at the base B of the transistor 204 becomeshigher than the voltage at the emitter E by approximately 0.6V orgreater, or if the voltage at the gate of the FET 204 b becomes higherthan the pinch-off voltage, the bipolar transistor 204 or the FET 204 bis activated.

At that time, in each of the rectification circuits, a current path isformed extending from the hot end of the detection winding Tc to thecold end of the detection winding Tc via the bias resistor 207 and thecollector C and emitter E of the bipolar transistor 204 (or the drain Dand source S of the FET 204 b) in order.

Because of this, a drop occurs in the voltage drop between the both endsof the bias resistor 207, and the FET 220 or the bipolar transistor 220b is forwardly biased and saturated. Then, a voltage which is almostequal to the source voltage is applied to the load 217.

When the polarity of the source voltage becomes negative and the voltageat the cold end of the secondary winding Tb becomes lower than thevoltage at the cold end of the detection winding Tc, the bipolartransistor 204 or the FET 204 b is reversely biased and inactivated.

At that time, the above described current path, from the hot end of thedetection winding Tc to the cold end of the detection winding Tc via thebias resistor 207 and the collector C and emitter E of the bipolartransistor 204 (or the drain D and source S of the FET 204 b) in order,is cut off, therefore, substantially no drop occurs in the voltagebetween the both ends of the bias resistor 207.

As a result, the FET 220 or the bipolar transistor 220 b is reverselybiased and inactivated. And the ground voltage is applied to the load217.

After such processing is repeated, a half-wave rectified voltage isapplied to the load 217.

Values, voltage values, or the like in the above described embodimentare just examples, therefore, they may be changed arbitrarily. If thebias voltage, the pinch-off voltage, or the like can not be obtained bya single diode, a Zener diode, a resistor, or the like, a plurality ofdiodes, Zener diodes, or resistors may be connected directly.

When an element, such as an MOSFET, through which a current large enoughto break the element cannot flow because of very high input impedance ofits control terminal, is used, the base resistor 206, or the like forregulating the current is unnecessary.

The switching power source according to the present invention maycomprise the structure shown in FIG. 54.

As illustrated, the switching power source comprises a transformer 302,an FET 303, an output terminal 308, resistors 311 and 312, bipolartransistors 313 and 314, base resistor 315, emitter resistor 316, and adiode 317.

The transformer 302 is the same as the transformer 2 in the firstembodiment. One end of the resistor 311 is connected to a hot end of asecondary winding Tb of the transformer 302, and one end of the resistor312 is connected to a cold end of a detection winding Tc. The other endof each of the resistors 311 and 312 is connected to base B of thebipolar transistor 313. A connecting point between the cold end of thesecondary winding Tb of the transformer 302 and the hot end of thedetection winding Tc is grounded. The hot end of the secondary windingTb is connected to source S of the FET 303.

The FET 303 is a p-channel MOS type FET. The source S of the FET 303 isconnected to the hot end of the secondary winding Tb of the transformer302 as described above. One end of the load 309 is connected to drain D,and the other end thereof is grounded. The bias resistor 307 isconnected between gate G and the drain.

The bipolar transistors 313 and 314 are NPN type bipolar transistors.

In the bipolar transistor 313, the base B is connected to the connectingpoint between the resistors 311 and 312 as described above, collector Cis connected to the source S of the FET 303, and emitter E is connectedto emitter E of the bipolar transistor 314.

In the bipolar transistor 314, collector C is connected to the gate G ofthe FET 303, and the emitter E is connected to the emitter E of thebipolar transistor 313 and one end of the emitter resistor 316. Theother end of the emitter resistor 316 is connected to an anode of thediode 317. A cathode of the diode 317 is connected to the cold end ofthe detection winding Tc. The base B of the bipolar transistor 314 isgrounded via the base resistor 315.

The number of turns of the detection winding Tc is the same as that ofthe secondary winding Tb or is simply in proportional to that of thesecondary winding Tb. Resistance values of the resistor 311 and theresistor 312 correspond to the turn ratio of the secondary winding Tb tothe detection winding Tc.

An operation of the switching power source will now be described.

When an alternating voltage which is output from an alternating voltagesource 301 is input to the both ends of a primary winding Ta of thetransformer 302, the output from the secondary winding Tb is supplied tothe load 309 via the FET 303.

Because of the power consumption at the load 309, when a load currentflows through the secondary winding Tb, the voltage between the bothends of the secondary winding Tb drops due to the resistance of thesecondary winding Tb and the magnetic resistance of the transformer 302.

At that time, because the load current does not flow through thedetection winding Tc, a circuit comprising the transistors 313 and 314,the base resistor 315, the emitter resistor 317 and the diode 317,switches the FET 303 in accordance with the relationship of thepotentials between the connecting point, between the resistors 311 and312, and the ground potential.

If the voltage drop at the secondary winding Tb increases because ofincrement of the load current, the bias which is applied to the gate Gof the FET 303 is controlled and strengthened so as to supply adequatepower to the load 309.

On the contrary, if the voltage drop at the secondary winding Tbdecreases because of decrement of the load current, the bias which isapplied to the gate G of the FET 303 is controlled and weakened so thatthe power to be supplied to the load 309 is reduced.

The channel type of the FET 303 is not limited to the p-type. An n-typeFET may be used. In this case, the bipolar transistors 313 and 314 arePNP type bipolar transistors.

Further, an arbitrary semiconductor switching element may be used forthe switching power source instead of the MOS type FET 303.

If a bipolar transistor, or the like, whose current path is opened/shutin response to flow of substantial quantity of current at a controlterminal is used, a current-limiting device such as a resistor may beinserted between the control terminal and the collector C of the bipolartransistor 314.

(Full-Wave Rectification Circuit)

Although the half-wave rectification circuit is mainly described in theabove embodiment, a full-wave rectification circuit may be comprised ofa combination of the half-wave rectification circuits.

That is, the full-wave rectification circuit may be comprised of thehalf-wave rectification circuits which are bridge-connected (they arerepresented by diodes in FIGS. 55(A) and (B)) as shown in FIG. 55(A).Moreover, the full-wave rectification circuit may be comprised of atransformer having a middle point in its secondary winding and twohalf-wave rectification circuits, as shown in FIG. 55(B).

Even in the full-wave rectification circuits shown in FIGS. 55(A) and(B), half-wave rectification circuits D1 to D6 are activated when thepolarity of voltages to be applied thereto are positive, and full-waverectified voltages are applied to loads.

Although the half-wave rectification circuit using the transistor singlyis described in the above embodiment, a plurality of transistors may beused. For example, FIG. 56(A) shows an example in which a plurality ofNPN bipolar transistors are connected parallel with each other, and acontrol circuit controls the activation/inactivation of the transistors.FIG. 56(B) exemplifies that a plurality of junction FETs are connectedparallel with each other, and a control circuit controls theactivation/inactivation of the FETs. FIG. 56(C) exemplifies that aplurality of N-channel junction FETs are connected parallel, and acontrol circuit controls the activation/inactivation of the FETs. Thesestructures can make the quantity of a switchable current which is pluraltimes larger than that obtained by the circuit using a singletransistor.

FIG. 57 exemplifies that a plurality of transistors are cascaded.According to this structure, the cascaded transistors areactivated/inactivated simultaneously, therefore, it is capable ofincreasing a withstanding voltage.

If multiple transistors are cascaded, a photo transistor 230 which isactivated/inactivated in response to lights may be used as thetransistor for example, and the control circuit may comprise aluminescent element 231 which luminesces lights foractivation/inactivation control as shown in FIG. 58, for synchronousactivation and inactivation of the transistor.

A Hall element may be used as the transistor. In this case, the Hallelement is connected between the power source and the load. The Hallelement is activated or inactivated by applying a magnetic field to theHall element in accordance with the result of the detection of thevoltage to be applied to the hole element or the polarity thereof.

Otherwise, an arbitrary semiconductor switching element, which isexternally controlled to be activated or inactivated, may be used.

A desirable transistor as the switching element has a small activationresistance and a high withstanding voltage while being inactivated.

A structure shown in FIG. 59, for example, whose emitter layer te andcollector layer tc have substantially the same thickness, may be usedfor the desirable transistor.

A field effect transistor whose source structure and drain structure arethe same as shown in FIG. 60 may be used.

FIG. 61 shows a comparison of the characteristics of the rectificationcircuit, which is structured as shown in FIG. 12, with an ordinalsilicon diode and schottky-barrier diode.

The result is obtained under the conditions wherein: the power from themains is used as a target voltage to be rectified; a load of 10A is usedas the load 17; an FET manufactured by FUJI ELECTRIC CO., LTD. whosemodel number is 2SK905 is used for as the MOSFET; the resistance valueof the resistor 23 is set to 100Ω; and an operational amplifiermanufactured by NATIONAL SEMICONDUCTOR CORPORATION whose model number isLM4558 is used as the OP-amp 21.

It is obvious from FIG. 61 that the half-wave rectification circuitshown in FIG. 4 can rectify the alternating voltage with a small lossbecause the voltage drop (the voltage between the emitter E and thecollector C) is approximately 0.01V in the half-wave rectificationcircuit shown in FIG. 4 when the transistor is activated, whereas thevoltage drop when a schottky-barrier diode is used is approximately0.4V, and the voltage drop when a silicon diode is used is approximately0.9V.

FIG. 62 shows a comparison of characteristics of the half-waverectification circuit structured as shown in FIG. 14, with the ordinalsilicon diode and schottky-barrier diode.

The result is obtained under the conditions wherein: the power from themains is used as a target voltage to be rectified; the load of 10A isused as the load 17; the FET manufactured by FUJI ELECTRIC CO., LTD.whose model number is 2SK905 is used for as the MOSFET; and windingratio of the current transformer is set to 1:100.

It is obvious from FIG. 62 that the voltage drop (the voltage betweenthe emitter E and the collector C) is approximately 0.6V immediatelyafter the polarity of the source voltage becomes positive andimmediately before the source voltage becomes 0V in the rectificationcircuit shown in FIG. 14, however, it is almost 0V over almost theentire period during which the polarity of source voltage is positive.On the contrary, the voltage drop is approximately 0.4V when aschottky-barrier diode is used, and is approximately 0.9V when a silicondiode is used. Therefore, the half-wave rectification circuit shown inFIG. 14 can rectify the alternating voltage with a small loss.

It has been proved from the first and second examples that therectification circuit of the present invention could rectify thealternating voltage efficiently with a small loss.

Industrial Applicability

As described above, the electric circuit according to the presentinvention is suitable for rectifying the alternating voltage andcurrent.

What is claimed is:
 1. A rectification circuit comprising: a transistor and a control circuit connected to said transistor, wherein said transistor comprises a current path and a control terminal, receives a target voltage to be rectified at one end of said current path, and outputs a rectified voltage at the other end of said current path by being activated and inactivated in accordance with control of said control circuit, said control circuit is connected to said current path and said control terminal of said transistor, and controls a signal to be supplied to said control terminal, in accordance with the direction of a current flowing through a node between the one end of said current path and an external circuit, thereby activating or inactivating said transistor to make said transistor rectify said target voltage, wherein said transistor serves as an inverse transistor when it is turned on.
 2. The rectification circuit according to claim 1, wherein said control circuit comprises: a current transformer having a primary winding connected to one end of said current path of said transistor and a secondary winding connected to said primary winding magnetically; and a circuit, connected to said secondary winding of said current transformer, for controlling a signal to be provided to said control terminal of said transistor, in accordance with a current in said secondary winding induced by a current flowing in a predetermined one direction through the primary winding, wherein the predetermined one direction is the same direction in which the rectified current flows.
 3. The rectification circuit according to claim 2, wherein said control circuit comprises means for converting the induced current flowing through said secondary winding into a voltage signal, and for applying the voltage signal to said control terminal.
 4. A rectification circuit comprising: a transistor and a control circuit, connected to said transistor, wherein said transistor comprises a current path and a control terminal, receives a target voltage to be rectified at one end of said current path, and outputs a rectified voltage at the other end of said current path by being activated and inactivated in accordance with control of said control circuit; and said control circuit is connected to said current path and said control terminal of said transistor, and controls a signal to be supplied to said control terminal, in accordance with the direction of a current flowing through a node between the one end of said current path and an external circuit, thereby activating or inactivating said transistor to make said transistor rectify said target voltage, wherein said control circuit comprises: a transformer having a primary winding connected to one end of said current path of said transistor and a secondary winding connected to said primary winding magnetically; and a circuit, connected to said secondary winding of said transformer, for controlling a signal to be provided to said control terminal of said transistor, in accordance with a current induced in said secondary winding, said control circuit comprises a conversion circuit for converting a current induced in said secondary winding into a voltage signal, and an amplifier which amplifies the voltage signal converted by said conversion circuit and applying the amplified voltage signal to said control terminal of said transistor.
 5. A rectification circuit comprising: a transistor and a control circuit, connected to said transistor, wherein said transistor comprises a current path and a control terminal, receives a target voltage to be rectified at one end of said current path, and outputs a rectified voltage at the other end of said current path by being activated and inactivated in accordance with control of said control circuit; and said control circuit comprises: a transformer having a primary winding connected to one end of said current path of said transistor and a secondary winding connected to said primary winding magnetically; a conversion circuit for converting a current induced in said secondary winding into a voltage signal; and an amplifier which amplifies the voltage signal converted by said conversion circuit and applying the amplified voltage signal to said control terminal of said transistor.
 6. The rectification circuit according to claim 5, further comprising a diode circuit which bypasses between one end of the current path and the other end of the current path of the transistor so that current flows in one direction through the primary winding until the transistor turns on.
 7. The rectification circuit according to claim 5, wherein said transistor comprises a bipolar transistor and the rectification circuit further comprises a diode circuit which is connected between the control terminal and one end of the current path and the other end of the current path of the transistor so that current flows in one direction through the primary winding until the transistor turns on. 